What type mouse are you using and how old is it?
About a week ago, I did a virus scan with Norton and found a few things that were automatically quarantined. I then deleted them, ran McAfee, Spybot, AOL anti-spyware stuff, and CCleaner. I've defragged about eight times, and everything should be fine from what I can tell (I'm not an expert!), but every second or so, my mouse stutters. The button is sticky, I can't drag and drop or scroll very well, because it won't drop stuff, and the audio and video both stutter at the same interval. What else can I do, besides wipe my HD and start fresh?