Power Supply issue. Possibly.

[KezariaK]

Hi, I'm fairly new here, but I am in need of some assistance. So I just installed my new parts for my computer. (A ATI Radeon HD 4890 and a 750 watt psu)
It worked fined for about a day, then i went on for a few minutes, then my computer shut down. I tried turning it on again, but i didn't respond. I felt some heat, but very little coming from inside the case. I think my PSU may have over heated, but I'm not too sure.
I am running Windows Vista x64, and I have a HP m9402f with the added parts above. Please help me! Thanks a ton. And merry christmas / happy holidays.

[Geek-9pm]

I  don't think it is the PSU. But maybe the new video card.
Do this.
Remove power cord.
Remove, carefully, the new ATI card you put into the HP desktop.
Put it back to the original configuration, the the video it came with. Plug power cord back it and try again.
What happens if you do that?