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My computer is slow: 5 common causes

Published on 10 November 2026 by Alain Zachayus

A computer that has become slow is not necessarily ready for the bin. In the vast majority of cases, the cause is one of the following five.

1. Too many start-up programs

Many programs start by themselves when you switch on the computer. In Windows, the Startup tab of Task Manager lets you disable those you don't need straight away.

2. An almost full disk

When the disk is more than 90% full, Windows slows down. Empty the recycle bin, delete unneeded downloads and use the Disk Clean-up tool.

3. An old mechanical hard drive

This is the most common cause on computers more than five years old. Replacing the hard drive with an SSD often makes the computer several times faster, at a moderate cost.

4. Unwanted programs or viruses

Toolbars, fake cleaners, ads that open by themselves: these programs eat up the computer's resources. A full scan and a browser clean-up often solve the problem.

5. Dust and heat

A computer that overheats slows itself down to stay safe. If the fan is constantly blowing hard, the dust needs cleaning out, especially on a laptop.

What if that's not enough?

Too little memory or a computer that is simply too old can also be the cause. During a remote maintenance session, I check these five causes and tell you honestly whether it is better to repair or replace.

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