i think its very possible that it is a registry issue. The same thing happened to the computer I am using now. Make a boot disk (find the stuff at
http://www.bootdisk.com, throw the things on a disk. Put the disk in the computer, and restart. Sooner or later, you will get to a prompt and type in "regscan /restore" and remember the space. You will get a list of early registry backups. Choose one from around the time the computer worked, and restart. It should now work
.
It's still possible that you are having a hard drive issue,
but this should help. It seems to me that the OS is booting, and
freezing at startup, which seems to be caused from a bad registry.
Don't exclude the fact that it *might* be power supply issue.
I have been experiencing that with Live Linux CDs on a laptop
where it just shuts down and leaves the screen powered on.
One last thing: If you have windows XP, at normal startup,
press F8 and open the advanced startup screen. You should
see an option for "Start with the last known good settings"
and you can select that. Hope you don't go insane.....