computer stops when booting..

Hi all, since hardware is less my domain, I thought I would post here so my fellow geeks may help me out .

Situation:
recently we had a blackout, so all electricity was gone for a while.
later that night, it got back on, but after 10 minutes it fainted again.

Now, I had switched a UPS in my desktop PC a long time ago, and of course it went beeping when we had the blackout. So I switched it off.

When I later that week wanted to boot my desktop, it got stuck in the boot sequence.
I could not use my keyboard, so booting up in safe mode is not an option....

I already opened the case but didn't notice anything special, besides some dust.

Any ideas, besides reinstalling Windows ? Because I fear I have to do this .. (if I can find my cd )

Thanks all .