My desktop has been freezing up off and on lately. I was watching tv (tv capture card) and browsing the web and it froze up so I had to restart then some off and on freezes for a few secs then fine (with the browser). I think its because lack of air flow and I certianly have enough memory (512MB) and no spyware or viruses on here. ANy thoughts? I have one fan in back plus cpu fan, no covwers off...