I got a good way to test weather its your hardware or your software I do this test all the time on my friends computers to help me troubleshoot issues. Here's what you can try:
1. boot into safe mode and mess around for a while and see if you freeze up
2. Get a linux livecd to boot from and play around and see if you get freeze ups
If both test do not show freezing I would assume its something wrong with the OS such as a virus or misconfiguration and not any particular hardware problem.
My all time favorite Windows fix is to reinstall it

so thats what I would suggest next, back up all your data first of course.