Computer restarts while browsing internet

Hey guys! I'm not sure where to go from here. I let my room mate use my computer while I was on vacation, and when I got back I found a ton of 'adult' adware and stuff all over it. I'm trying to get my computer back into shape, and i'm 90% there, but there's just one issue i'm having trouble with. Occassionally while i'm browsing the internet, my computer will reset if I click on a link or while loading up a web page. I first thought that maybe a virus that was downloaded by him corrupted one of the internet files, resulting in it crashing my computer instead of my ie.

I uninstalled ie, reset my computer, and reinstalled it, but i'm having the same issue. I tried downloading firefox and navigator to see if it's a computer issue or an IE issue, and whenever I try to install those programs i get an error "error opening file for writing: C:\Program Files\Mozilla Firefox\components\nsHelperAppDlg.js" and then I have to cancel installation. I did a full system scan with both ad-aware and kaspersky antivirus, and both say it's clean. I've tried to uncheck automatic restart for critical system failures to see if I can get more information, and all that did was cause it to freeze instead of restart. I also tried the reset button on advanced tab in ie's tools and that also caused my computer to crash. oh, by the way i'm running windows xp and its happening with ie7.

any suggestions?