Heres an a great site that will walk you through some general mainenance, you would be surprised how well some of these will work.
The first thing I want you to try is"
Start>Run>cmd Start a command prompt.
Run "sfc /scannow"
this is a System File Check and will try to find some common issues with your OS.
Also when this completes I would run "chkdsk /r" This will check the integrity of the HDD the next time you start your computer.