hmmm what your first described was your power supply what it sounds like but if you getting to windows Loading screen and it freezes it would sound like a hard drive failure. Usually you can tell by a hard drive failure if you start hearing a ticking noise. I would recommend seeing if you can get it to boot to BIOS screen or a Boot CD and let it sit for a few min.... this way you can tell if the Power supply is failing.
Specifically look at the Power supply Fan itself see if its causing it to overheat

Im really leaning towards the Power supply over-heating or just dieing.