Performance
March 31, 2026 10 min read IT Cares Tech Team

Why Is My Computer So Slow? 8 Causes & How to Fix Them

A slow computer is one of the most common — and most frustrating — tech problems Canadians deal with every day. The good news: in most cases, you do not need a new computer. You need to identify and address the specific cause. This guide walks through the 8 most common reasons computers slow down, with practical solutions for each.

Table of Contents

  1. Too Many Startup Programs
  2. Full or Fragmented Hard Drive
  3. Malware or Virus Infection
  4. Outdated Operating System or Drivers
  5. Insufficient RAM
  6. Too Many Browser Extensions
  7. Failing Hard Drive
  8. Overheating
  9. Frequently Asked Questions

Before diving into the individual causes, open Task Manager (press Ctrl + Shift + Esc on Windows) or Activity Monitor (Mac: Applications › Utilities). Look at the CPU, Memory, and Disk tabs. The column that shows a very high percentage is almost certainly your problem.

1 Too Many Startup Programs

Every program that launches when you start Windows consumes CPU and memory during boot — and often continues running in the background all day. If your computer is slow to start and sluggish for the first 10–15 minutes after boot, this is almost always the culprit.

Common offenders: Spotify, Discord, Skype, Steam, OneDrive, Dropbox, iTunes, Adobe updaters, printer software, and manufacturer "helper" apps that came pre-installed.

How to fix it:
  1. Press Ctrl + Shift + Esc to open Task Manager
  2. Click the Startup tab (Windows 10/11)
  3. Review each item. Right-click anything you do not need immediately at startup and select Disable
  4. Restart and notice the difference

On a Mac: System Settings › General › Login Items › remove items you do not need.

2 Full or Fragmented Hard Drive

Windows requires free disk space to create temporary files, manage virtual memory, and install updates. When your drive reaches 85–90% capacity, performance drops noticeably. At 95%+ full, your computer can become nearly unusable.

Traditional spinning hard drives (HDDs) also benefit from defragmentation, which reorganises fragmented files so they can be read more quickly. SSDs do not need defragmentation but should still be kept from filling up completely.

How to fix it:
  1. Open Settings › System › Storage to see what is taking space
  2. Run Disk Cleanup (search for it in the Start menu) — select "Clean up system files" for maximum effect
  3. Empty the Recycle Bin and Downloads folder
  4. Move large files (videos, photos) to an external drive or cloud storage
  5. For HDDs: search "Defragment and Optimise Drives" and run it
Quick win: The Temporary Files section in Storage settings can often free up 5–15 GB on an average computer. Always check here first.
3 Malware or Virus Infection

Malware is one of the most common yet overlooked causes of a slow computer. Infections that run silently in the background — cryptominers using your GPU, spyware logging your keystrokes, or adware serving ads — consume enormous resources without any visible window on screen.

A cryptominer infection, for example, can push your CPU to 90–100% usage continuously, making everything else on your computer crawl. Many Canadians assume their computer is "just old" when in fact it has been secretly mining cryptocurrency for someone else.

How to fix it:
  1. Download Malwarebytes Free and run a full scan
  2. Run Windows Defender full scan from Windows Security
  3. In Task Manager, look for processes with unfamiliar names using high CPU
  4. If you find threats or the infection keeps returning, book a professional remote virus removal
4 Outdated Operating System or Drivers

Running an outdated version of Windows or macOS means you are missing performance improvements, security patches, and bug fixes that Microsoft and Apple have released. Outdated device drivers — particularly for your graphics card and storage controller — can also cause stuttering and slowdowns.

Conversely, if your computer just performed a major update, it may run slowly for 24–48 hours while Windows indexes files and completes background optimisation tasks. Give it time before concluding something is wrong.

How to fix it:
  1. Windows: Settings › Windows Update › Check for Updates
  2. Device Manager: right-click on Display Adapters and choose "Update driver"
  3. Mac: System Settings › General › Software Update
  4. Consider upgrading from Windows 10 to Windows 11 if your hardware supports it (free upgrade)
5 Insufficient RAM

RAM (Random Access Memory) is your computer's short-term working memory. When you run more programs than your RAM can hold, Windows moves some data to the hard drive (called "virtual memory" or "paging"). Accessing the hard drive is far slower than RAM, causing noticeable slowdowns — especially when switching between applications.

For modern Windows 11, 8 GB is the practical minimum for everyday use. If you have 4 GB or less and run a browser with multiple tabs, you will almost certainly run out of RAM regularly. 16 GB is recommended for comfortable multitasking.

How to fix it:
  1. Check current usage: Task Manager › Performance › Memory
  2. If consistently above 85%, a RAM upgrade is worth considering
  3. Reduce browser tabs — each tab can consume 100–300 MB of RAM
  4. Close programs you are not actively using
  5. If your computer has only 4 GB, a RAM upgrade (typically $40–$80 CAD) can make it feel like a new machine
6 Too Many Browser Extensions

Browser extensions run in the background on every web page you visit. Even a single poorly-coded extension can consume hundreds of megabytes of RAM and push CPU usage up significantly. Having 10–20 extensions installed is not unusual, but it has a measurable impact on browsing speed and overall system performance.

Extensions that are known to cause slowdowns include ad blockers with large filter lists, social media widgets, screenshot tools, grammar checkers, and VPN extensions that encrypt every request.

How to fix it:
  1. Chrome: Menu › Extensions › Manage Extensions — disable or remove anything you do not use daily
  2. Edge: Menu › Extensions › Manage Extensions
  3. Firefox: Menu › Add-ons and Themes
  4. Test by opening a private/incognito window (extensions are disabled by default) — if the browser is suddenly faster, an extension is the cause
7 Failing Hard Drive

A hard drive that is beginning to fail causes some of the most dramatic slowdowns. When the drive develops bad sectors, Windows has to repeatedly retry reading data — what normally takes milliseconds can take several seconds. Programs freeze briefly and unpredictably. Files take a very long time to open or save.

This is a warning sign you should not ignore. A failing hard drive will eventually stop working, potentially causing complete data loss. If your computer is more than 3–5 years old and has a spinning HDD, this is worth checking immediately.

How to check and fix:
  1. Download CrystalDiskInfo (free) — it reads your drive's health status directly
  2. A "Caution" or "Bad" result means the drive is failing and should be replaced soon
  3. Back up your important files immediately if you see any warnings
  4. Replacing an HDD with an SSD is the single most impactful upgrade for an older computer — boot times can go from 90 seconds to under 15 seconds
Do not delay: If CrystalDiskInfo shows warnings, back up your files today. Failing drives can fail completely without further notice.
8 Overheating / Thermal Throttling

Modern processors automatically reduce their speed when they get too hot — a protection mechanism called thermal throttling. When a CPU hits 90–100°C, it can drop to half or even a third of its normal speed to prevent permanent damage. The result feels like a sudden dramatic slowdown, especially during demanding tasks.

Overheating is usually caused by dust buildup blocking the cooling vents, a dried-out thermal paste between the CPU and heatsink (common in laptops older than 3–4 years), or using the laptop on a soft surface that blocks the air intake.

How to fix it:
  1. Download HWiNFO64 or Core Temp to monitor temperatures in real time
  2. Use your laptop on a hard, flat surface — never on a bed or couch
  3. Use compressed air to blow dust out of vents (do this every 12–18 months)
  4. A laptop cooling pad ($20–$40 CAD) can reduce temperatures by 5–15°C
  5. For severe overheating, thermal paste replacement requires a professional — a service IT Cares can arrange

Quick Diagnosis Summary

Not sure where to start? Use this quick reference:

Frequently Asked Questions

Why did my computer suddenly get very slow?
Sudden slowdowns are most often caused by a new program launching at startup, a Windows update running in the background, a malware infection, or a hard drive that has just reached critical capacity. Open Task Manager (Ctrl+Shift+Esc) to see which process is consuming your CPU or memory at that moment.
Will adding more RAM fix a slow computer?
RAM upgrades dramatically improve performance if your computer is slow because it is running out of memory. If Task Manager shows memory usage consistently above 85–90% during normal use, more RAM will make a noticeable difference. However, if your slowness is caused by malware, a failing hard drive, or too many startup programs, more RAM will not help — address the root cause first.
Does a full hard drive really slow down a computer?
Yes, significantly. When a hard drive reaches 85–90% capacity, Windows struggles to create temporary files and virtual memory pages, causing dramatic slowdowns. Aim to keep at least 15% of your drive free. On an SSD, keeping 10–20% free maintains optimal performance.
How do I check if malware is making my computer slow?
Open Task Manager and look for processes consuming high CPU or memory that you do not recognise. Download Malwarebytes Free and run a full scan. Signs that strongly point to malware: high CPU usage even when the computer is idle, browser redirects, pop-up ads appearing outside the browser, and your antivirus suddenly being disabled.
How many startup programs is too many?
Most computers should have no more than 5–10 startup programs. If you have 20 or more items launching at startup, your computer will be slow to boot and sluggish for the first 5–10 minutes. Disable anything you do not immediately need at startup — you can always open programs manually when needed.
Can overheating cause a slow computer?
Yes. When a CPU reaches its temperature threshold (typically 90–100°C), it automatically reduces its speed to prevent damage — thermal throttling. This can make your computer feel dramatically slower. Signs of overheating include a loud fan, the computer being hot to the touch, and performance improving once the computer cools down.
Should I use a registry cleaner to speed up my computer?
No. Registry cleaners are largely ineffective and can cause serious damage if they delete the wrong entries. Microsoft does not recommend them. Focus instead on the proven solutions: removing startup programs, clearing disk space, scanning for malware, and keeping Windows updated.
How much does it cost to have a slow computer professionally fixed in Canada?
IT Cares charges $99 for a full remote speed optimisation session, which includes startup cleanup, malware scan, disk optimisation, and OS updates. The Complete Tune-Up at $149 adds backup setup and a full security audit. Both are flat-rate prices with a fixed-or-refunded guarantee.

Let Us Fix Your Slow Computer — Today

IT Cares certified technicians diagnose and speed up computers remotely, across Canada. No appointment needed — most sessions start within 2 hours.

Book a Speed Optimisation Session (581) 398-1270

Related: Can a Virus Be Removed Remotely? • Best Free Antivirus for Canadians • Remote IT Support for Individuals