The system could be slowed down for a number of reasons. Most commonly this problem exists due to large amounts of spyware and/or adware on your computer.
The first step in solving this issue is installing anti-spyware software from the network that will help you delete these “mini programs.” (Example: Ad-Aware)
1. You should often clean up temporary files folder.
This is because that several different applications will produce some temporary files by using the Windows. If you don’t clean up temporary files folder in time, the disk space will be occupied by these temporary files and the speed will be dropped.
2. Run two or three free web-based AV scanners. – Go to web-based AV scanners
(This scanning is the most time-consuming step in this checklist, but it is important.)
Record the exact malware names, and file names and locations, of any malware the scans turn up. Quarantine then cure (repair, rename or delete) any malware found.
Hope this will help you to speed up your computer system.