Slow computer? 8 causes and how to fix them

A computer that was fast two years ago now takes three minutes to start up and opening Excel feels like an eternity. Does this sound familiar? Before you consider buying a new computer, read this article. In many cases, the problem can be resolved quickly and for a fraction of the cost of a new machine.

1. Old hard disk drive (HDD) instead of SSD

Symptoms: Slow system startup, long programme loading times, and the hard drive running at 100% even during normal use.

Why this happens: A classic hard disk drive (HDD) with rotating platters is the slowest component in a computer. If your computer still runs on an HDD, this is most likely the main cause of its slowness.

Solution: Replacing an HDD with an SSD is the most effective upgrade available. The computer speeds up dramatically. It boots in 15-20 seconds instead of three minutes, and programs open instantly. A 500 GB SSD costs around 1 000 Kč. Including data transfer and installation, expect to pay between 1 500 and 3 000 Kč.

2. Insufficient operating memory (RAM)

Symptoms: The computer slows down when multiple programs are opened simultaneously; you have to wait when switching between windows.

Why this happens: Operational memory is the computer's working space. Every open program occupies a certain amount of RAM. When memory is full, the system starts using the disk as backup memory (swap), which is orders of magnitude slower. For standard office work you need at least 8 GB, preferably 16 GB of RAM.

Solution: Adding RAM is simple and relatively inexpensive. An 8 GB DDR4 module costs around 500-800 Kč. In most desktop computers and some laptops, memory can be easily upgraded.

3. Malware and unwanted software

Symptoms: The computer is slow without an apparent cause, pop-up ads appear, the browser behaves strangely, and unknown programs are present in the system.

Why this happens: Malware (viruses, adware, spyware) runs in the background and consumes computer performance. Some malicious programmes mine cryptocurrencies, send data to attackers or simply slow down the system with advertising modules.

Solution: Run a thorough scan with an antivirus program. We recommend downloading Malwarebytes (the free version is sufficient for a one-off check) and performing a full system scan. If you suspect a more serious infection, it is better to leave it to a professional to prevent the issue from recurring. For more information on protection, see the article about IT security for companies.

4. Too many programmes at startup

Symptoms: The computer takes a very long time to start up; after logging in, it takes minutes before it is ready for work.

Why this happens: Many programs launch automatically when Windows starts, Skype, OneDrive, Spotify, Adobe Updater, printer drivers and dozens more. Each one consumes time and resources.

Solution: Open Task Manager (Ctrl+Shift+Esc), click the "Startup" tab and disable everything you do not need. Keep only antivirus, OneDrive (if you use it) and drivers that are actually required. Disabling a program at startup does not delete it. You can still launch it manually when needed.

5. Missing system update

Symptoms: The system is generally slower, applications occasionally crash, and security warnings appear.

Why this happens: An outdated system suffers from errors that Microsoft continuously fixes. Some updates include performance optimisations. On top of that, an obsolete system poses a security risk.

Solution: Open Settings and go to Windows Update. Install all available updates. This may take up to an hour and require a restart, but it is important for both performance and security.

6. Overheating (thermal throttling)

Symptoms: The computer is slow mainly during demanding tasks, the fans run at maximum speed, and it is hot to the touch.

Why this happens: When the processor exceeds a safe temperature, it automatically reduces its performance to prevent damage. This is known as thermal throttling. The usual causes are dust in the coolers, dried-out thermal paste or a faulty fan.

Solution: The computer needs cleaning. A competent user can clean a desktop PC using compressed air. Laptops are more complex, disassembling a laptop without experience is not recommended. Replacing the thermal paste and cleaning the heatsink will restore the computer's original performance. This costs 600-1 200 Kč at a service centre.

7. Full disc

Symptoms: Warning about insufficient disk space, slow file operations, inability to save new files.

Why this happens: Windows requires free disk space for temporary files, virtual memory and updates. When the disk is more than 90% full, the system begins to slow down significantly.

Solution: Launch the "Disk Cleanup" tool in Windows (press Win, type "disk cleanup"). Delete temporary files, the Recycle Bin, and old updates. Move large files (photos, videos) to an external drive or the cloud. If the drive is too small, consider replacing it with a larger SSD.

8. Outdated hardware

Symptoms: The computer remains slow even after all the steps mentioned above and is older than 6-7 years.

Why this happens: Software demands are increasing. Operating systems, browsers, office applications, everything becomes more demanding with each new version. A processor from 2018 simply cannot keep up with what is expected of it in 2026.

Solution: In this case, replacing the computer is more economical than repairing it. A new business computer with an SSD and 16 GB of RAM costs from 12 000 Kč. We will transfer data and settings from the old computer. More information on when to repair and when to replace can be found in our article about computer servicing in Prague.

Where to start

If your computer is slow, try points 4 and 5 first, disabling unnecessary startup programs and updating the system. You can do this yourself at no cost.

If this does not help, the most likely cause is an old HDD drive (point 1) or insufficient RAM (point 2). Replacing it with an SSD is the best investment you can make in an older computer.

And if you are unsure or do not want to take a risk? As IT service in Prague 1 We will carry out diagnostics and tell you exactly what the computer needs.