User accounts disabled (Windows XP)

Hello,
After getting rid of numerous viruses on my HP computer, I still had no internet access. I used AVG's repair function to repair basically everything and then was able to access the internet after days of effort. I updated my virus definitions for Norton and AVG, deleted a lot of viruses and received messages from both saying my computer was completely protected. Just as i was shutting my computer down, thinking it was fixed, a Norton anti-virus message came up about a Trojan Vundo virus. I shut down anyway (it was 2am), thinking I could run another scam in the morning. Now when I turn the computer on, a welcome screen appears with my account name (which it has not done for over a year) and when I click on it, it says "loading your personal settings", then it very quickly changes to "saving your settings" and "shutting down". My only option is to stand by, restart or turn off the computer. In essence, all I can do is turn the computer on and off. Even in safe mode, or last good configuration, nothing works. I tried reinstalling the windows xp installation cd and choosing repair, it didn't change anything. I am going absolutely crazy...especially since I actually had it working last night and today it's useless...any advice greatly appreciated!!!