I would do some spyware scans just to eliminate that possibility, then do some other performance tweaks..
goto start>run>msconfig
go to the startup tab and uncheck anything that you dont need running all the time.
how long have you had this rig? you may wanna do a defrag on your hard drive.
right click my computer>click manage> go to Disk defragmenter.. self explainatory from there.
See if that helps out a bit.