Somethings wrong with my pc....

If anyone here could help me i would really appreciate it. Im running windows xp service pack 2.

When i started my pc up today it froze at the windows start up screen and my screen went black.

I restarted my computer in safe mode. In safe mode its starts up fine. I ran a thorough virus scan using avast home edition, it came back clear. I then did another scan using spybot search and destroy which also came up clear. I then did an online virus scan at www.bitdefender.com which came back clear.

I decided to try a system restore, i did this and windows managed to boot up. I then restarted the computer to see if the problem was fixed, but again my pc froze at the same point.

I restarted and did another system restore to get windows back up again. I had recently installed winamp, so i decided to uninstall and delete it just in case it was causing a problem, i deleted several other programs i don’t use anymore as well. I did a disk clean up to get rid of all my temporary files. I then decided to do a defrag, my drive was very fragmented but the defrag fixed it. I restarted my pc to see if it would work.

This is what now happens:

It gets up to the screen which has the windows icon and a loading bar underneath.

Screen goes black, freezes, switches off, then comes back on again at the windows welcome screen, the computer freezes on this screen, if i leave it for 5 to ten minutes windows will eventually boot up.

Thanks for taking the time to read this. Any idea what could be going wrong?