1. Update the definitions of your anti-virus and run a complete scan of your hard drive in Safe Mode. Resolve any unfixable issues. Note that some viruses require additional steps before they can be removed; usually a websearch will find specific instructions or a special removal tool.
2. If the sluggishness is sudden, and you have recently downloaded an application, the problem may reside there. Test this by completely removing it. A wise user will generally perform a websearch about the application before downloading it because in most cases, any potential problem with malware or poor performance will have surfaced.
3. Adware and Spyware can drastically effect your computer’s performance, and these are all over the Internet. A very recent study indicated that one out of every 20 executable files on Web sites is spyware, and 1 in 25 domains contain at least one piece of spyware waiting for victims.Update the definitions of your anti-spyware applications and scan your hard drives in Safe Mode. Experienced users will regularly run two or three of these applications, because each company has its own criteria for what constitutes spyware and will only search against their own set.
4. Review applications that self-launch on startup.If, for example, you have Spybot Search and Destroy, you can use its startup tool that lists startups and allows you to turn off any you do not need.
5. Clean up your hard drive. Delete unused programs and transfer old files to a CD. Unplayed games, lots of family pictures, zipped files that you have already opened, applications you have not used in two years, software for that old printer you threw away last year---these are some examples of files you can delete. Then use Window’s Disk Cleanup to delete temporary internet files, temporary PC health files, etc..
6. Run scandisk/checkdisk in Safe Mode. Have it repair anything it finds.
7. Defragment your computer. Windows tends to put new files in any available open space; defragging will place associated segments of files closer together so your read arm has less travelling around the hard drive to do, saving wear and tear while speeding up programs.