Windows does not start unless in safe mode.

[Guest]

My brother was playing a game, which warned him via an error message that my
computer's processor couldn't handle it, but he played it anyway. It worked
fine for about five minutes but then locked up, and the task manager wouldn't
open. I restarted the computer by holding down the power button, and it went
to the screen that shows the Windows XP logo with a small loading bar near
the bottom and will not proceed from there unless I tell it to start up in
safe mode.

 

[Pegasus \(MVP\)]

My brother was playing a game, which warned him via an error message that my
computer's processor couldn't handle it, but he played it anyway. It worked
fine for about five minutes but then locked up, and the task manager wouldn't
open. I restarted the computer by holding down the power button, and it went
to the screen that shows the Windows XP logo with a small loading bar near
the bottom and will not proceed from there unless I tell it to start up in
safe mode.

Start in Safe Mode and run msconfig.exe. Now disable the various
tasks under Startup tab until you find the culprit.