I have microsoft antispyware
That's usually not enough. While spy/adware might be the problem, I doubt it can cause one program to perform that poorly. Check out this
thread for Spybot Search & Destroy and Ad-Aware SE Personal 1.06. Download them, update the definitions like you would in Norton, then full scan your system when you have a chance, then update and scan about once per week or even once a month if you're lazy. Seeing as you bought your computer three years ago, the hard drives should be at least 5,400 and shouldn't have a problem in this situation. The last thing I can think of is to check out the program's developers to be sure they're legit.