The first thing to do when a computer suddenly slows down is to shut it down. Make sure it is completely powered off, and then restart it. This will typically fix any random, non-repeatable problems.

Also, make sure that it is the computer itself that is running slowly, and not your internet connection. Network congestion and problems with ISPs can look like a problem with the computer itself, but are not fixable on your end. If the problem re-occurs after rebooting, then there are a variety of things that could be going on which can be looked at by a user with no technical training.

1) There may be a program of some kind which is suddenly going out of control, using up memory and CPU time. Close all your running programs one by one, and see if the problem goes away when a certain program is closed. If all of the running programs are closed and the computer is still running slowly, then it may be one of the programs which are running all the time, such as anti-virus programs, and other tools with icons that typically reside in the system tray (in the lower right corner by the clock). Some of these programs can be exited or disabled by right-clicking on their system tray icon, but some of them may need to be uninstalled.

 2) Run a spyware/malware check using a trusted scanning tool. Malicious software can often use up computer memory and other resources in order to perform whatever tasks its creator gave it, and will often not show up in any list of programs to close or uninstall.

3) The system may be overheating and causing the CPU to slow down in order to avoid damaging itself. This is typically caused by bad ventilation or defective fans. Make sure that nothing is covering up air intakes or outputs. Opening up the computer to see if there are any broken cooling fans may void your warranty, so contact your computer manufacturer first if you believe this may be the case.

4) The computer’s memory may have developed a fault, causing the computer to stop using the defective memory stick. Check how much memory your computer says it currently has, and compare that to how much memory it should actually have. If it is smaller, contact your computer manufacturer for instructions.

5) A peripheral device may be malfunctioning. Try shutting down the computer and disconnecting all non-vital equipment, like scanners, external hard drives, USB thumb drives, webcams, printers, etc. If the problem goes away, reconnect them one by one and see which one causes the problem to return.