Two days ago, woke up, saw that my computer was running a bit slow, so I rebooted it. It gets to the starting up screen but then when it's done, instead of logging me in, the screen goes fizzy and then it shuts down. I've tried over and over but it won't get past that stage. I'm able to start it up in safe mode but at a loss as to what to do next. The things I've tried are: booting with Win2k cd and trying the Fast Repair, downloaded the sophos sasser detection software but didn't detect sasser. I think the last time I did a Windows patch was about a month ago and I also run Avast Anti-virus and Sygate Personal Firewall. Any help would be appreciated.

Revert to an old copy of the registry if you have one. http://support.microsoft.com/default.aspx?kbid=322755

I had this problem one time it ended up being a corrupt video driver. Remove and reinstall video card driver.