Are you able to get into safe mode at all?

http://www.computerhope.com/issues/chsafe.htm#03
Getting into Windows Safe Mode.

http://windows.microsoft.com/en-AU/w...t-is-safe-mode
What is safe mode?

I had a similar problem as you described in the first paragraph but I was running xp pro, not vista.
Turned out to be some sort of major error which was described as a "loop". It beat me unfortunately.

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p.s. you should have bought a mac.