My computer is low - Microsoft Windows

The most common reason for slow processing speed is insufficient RAM memory.

Increase the RAM, if RAM available is no more than 512MB, then it must be upgraded.

Check also your hard drive state. If you have less than 1GB free, that will slow down the system. Go to Start>>Programs>Accessories>System Tools>Disk Defregmenter and do a Defrag of the hard disk.

If you have at least 1 GB RAM, and you took care of the hard drive, then you can check the process starting up on their own and remove the useless one, or spot mala-ware that can affect speed. You can use a software like Hijack This, and search on google te function of each process started on the list reported by the software.

You can download Hijack this here MajorGeeks | If download does not start, then click at the top of the page, where it says Click Here If It Does Not.
Be careful if you delete the wrong files using this software you can harm the system, and Windows may not work properly.

If you think you have malaware you can also install Spy Bot, and do a system scan. Download Spybot from The home of Spybot.

If all the above does not work, and there is no malaware, then you usually reinstall the system.

Check also the bios settings, BIOS can downgrade the CPU speed on default , even if this is uncommon on recent BIOS.

If a computer is still slow with a fresh system and enough resources then it is one of those rare occasions when you have an hardware fault.
Hardware that can cause slow down is: RAM CPU Motherboard HD Video card.

Some tips on procedure can damage your windows installation. Do not download Hijackthis software and do not change BIOS settings and do not touch hardware unless you are sure of what you are doing.