Try some general maintinance for a start,
firstly, Do a Disk Cleanup.
Then do a Defragmentation.
This will put all files etc. back into order & may solve your problem.
Recently I've been noticing a strange minor problem. Whenever I click Start->Log off->Switch User, nothing happens. No error messages or anything. The screen just goes back to what it was doing. I don't know if this is the Fast User Switching thing or not. It says automatic under startup type in the computer management window. And I just scanned with Ad-aware, Spybot, and Microsoft Antispyware to see if there were any bugs. All found were removed but problem remained. If anyone knows how to fix my problem, please help. Thanks.