A sluggish computer is one of the most frustrating things to deal with — but in most cases, it’s fixable without spending a penny. Here’s what’s likely causing it and exactly what to try first.

How to use this guide

Work through the sections below in order. Each one covers a common cause of slowness, starting with the most likely culprits. If you fix the problem partway through, great — no need to read further. If you get to the end and your computer is still struggling, there’s a section at the bottom on when it’s time to call in a professional.

1. Too many programs starting up with Windows

This is the single most common cause of a slow computer, especially one that takes ages to be usable after you turn it on.

Every time your computer starts, Windows loads a list of programs automatically in the background — things like Spotify, OneDrive, Skype, printer software, and dozens of others that have quietly added themselves over time. Most of these you don’t need immediately, and they all eat into your memory and processor.

How to fix it:

1. Press Ctrl + Shift + Esc to open Task Manager
2. Click the Startup tab (in Windows 11, it may say Startup Apps)
3. Look at the Status column — anything marked “Enabled” runs every time Windows starts
4. Right-click anything you don’t need immediately and select Disable

Safe things to disable include: Spotify, Teams, Skype, OneDrive (if you don’t use it), Adobe updaters, and any manufacturer software like HP Support Assistant. Do not disable anything from Microsoft or your antivirus.

2. Not enough free storage space

Windows needs free space on your hard drive to work properly — it uses it as temporary workspace while you’re running programs. When your drive gets too full (generally below 10–15% free space), everything slows down noticeably.

How to check:

1. Open File Explorer
2. Click This PC on the left
3. Look at the bar under your C: drive — if it’s red or nearly full, this is your problem

How to fix it:

• Search for Disk Cleanup in the Start menu and run it — tick everything including “Temporary files” and “Recycle Bin”
• Go to Settings → System → Storage and turn on Storage Sense to automatically clean up temporary files
• Move large files (photos, videos) to an external hard drive or cloud storage
• Uninstall programmes you no longer use via Settings → Apps

3. Your computer needs a restart (or has been hibernating too long)

This sounds obvious, but it’s worth saying: many people leave their computers on sleep or hibernate for days or weeks without a proper restart. Over time, memory fills up with background processes and temporary files that only clear on a full restart.

The fix: Shut down completely (not sleep, not hibernate — Shut down), wait 30 seconds, then turn it back on. If this makes a noticeable difference, make it a habit to do a full restart every few days.

4. Malware or a virus running in the background

Viruses and malware often don’t announce themselves — they just quietly use your processor and internet connection in the background, making everything feel sluggish.

Signs this might be your problem:

• Your computer slows down suddenly, not gradually over time
• Your internet feels slow even when your broadband is fine
• You see pop-ups or your browser behaves strangely
• Your hard drive light is constantly on even when you’re not doing anything

What to try:

Windows has a built-in tool called Windows Security (search for it in the Start menu). Run a full scan — it’s free and reasonably effective. If it finds something, follow its instructions to remove it.

If the scan comes back clean but you still suspect something is wrong, a free tool called Malwarebytes (available at malwarebytes.com) is excellent at finding things Windows Security misses.

⚠️ Important: If you’re not confident removing malware yourself, it’s worth getting a professional to do it. Incomplete removal can leave your computer vulnerable. Book a virus removal service →

5. A hard drive that’s old or starting to fail

Traditional hard drives (HDDs) — the kind with spinning disks inside — slow down significantly as they age, usually after 4–5 years of use. They can also develop bad sectors, which causes the computer to pause and stutter as it works around damaged areas.

How to check:

Download a free tool called CrystalDiskInfo (crystalmark.info). When you open it, look at the Health Status field:

• Good — your drive is fine
• Caution — the drive is showing early warning signs; back up your files immediately
• Bad — the drive is failing; stop using it and seek professional help

If your computer has an older HDD, replacing it with a modern SSD (solid state drive) is the single most effective upgrade you can make. Most computers feel brand new afterwards. See our guide: Should I upgrade my RAM or switch to an SSD?

6. Not enough RAM

RAM (Random Access Memory) is what your computer uses to keep programmes open and running. If you don’t have enough, Windows starts using your hard drive as a substitute — which is much, much slower.

Signs you’re running low on RAM:

• Your computer slows down when you have several browser tabs open
• You hear a lot of hard drive activity (clicking or whirring) when switching between apps
• Task Manager shows memory usage above 80–90%

How to check:

Open Task Manager (Ctrl + Shift + Esc), click Performance, then Memory. Look at the In Use figure compared to the total available.

Most modern Windows computers need at least 8GB of RAM to run comfortably. If you have 4GB or less, upgrading is worth considering.

7. Windows or drivers need updating

Outdated Windows versions and old device drivers can cause performance problems and instability. Windows updates also include security patches that prevent malware from exploiting your system.

How to check for updates:

Go to Settings → Windows Update and click Check for updates. Install everything available, then restart your computer.

When to call a professional

If you’ve worked through all of the above and your computer is still slow, it’s likely one of the following:

• A failing hard drive that needs replacing
• Malware that’s resistant to standard removal tools
• Hardware that’s genuinely too old or underpowered for modern Windows
• A deeper software problem like a corrupted Windows installation

Dave at Computer Repair Bolton offers free diagnostics — so if you’re not sure what’s wrong, bring it in and we’ll tell you exactly what the problem is before you commit to any repair. No fix, no fee.

Book a free diagnostic →

Summary

Cause	Difficulty to fix yourself	Likely cost if professional needed
Too many startup programmes	Easy	Free
Full hard drive	Easy	Free
Needs a restart	Easy	Free
Virus or malware	Moderate	From £30
Old or failing hard drive	Hard	From £60 (SSD upgrade)
Not enough RAM	Hard	From £40
Outdated Windows	Easy	Free

Still not sure what’s wrong? Contact Dave at Computer Repair Bolton for free advice — no jargon, no obligation.