Solved Computer Restarting at Start-up

Hey there,
I am working on my mothers computer. She has a dell inspiron 1525 running windows vista basic.
She is having a huge problem. Whenever she starts her computer, it starts up normally, and goes all the way to the log in screen. You can log in and everything seems fine. It takes about 30 seconds from the time that it shows the accounts to choose from until it automatically restarts. I let the battery completely drain and am recharging it. It is still auto restarting. Her AV was up to date and no problems there. Im sure becasue i hound her about it! Haha.
Anyways, does anyone have any ideas?

She needs this for work tomorrow so the sooner the help the better.
Thanks so much everyone,
Ben

Can you reboot to safe mode? If yes, you can try looking at msconfig and disabling startup items you are POSITIVE will do no harm. do NOT uncheck windows files.

Thanks lemur, but i aslready fixed it. It was crazy and i am kicking myself in the @$$ for this one.
All i had to do was install the Vista DVD at start-up, boot from it, and vista did the rest. Not sure what was wrong but i fixed it that way.

Thanks a ton,
Ben