So after unattaching everything again in order to run that power supply tester, and reattaching everything, my PC powered on and stayed on. Unfortunately I didn't have a monitor or peripherals...

No beeps from the motherboard.

Power supply seems to be working, I used one of those Antec power supply testers and everything is all green. Should I go ahead and try your method of testing it...

The six pin cable is connected directly from the power supply to the 7950GT, yes. I've made certain all the cables are firmly attached to the power supply, and everything they're connected to.
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Some more information:

1. The power supply is less than a month old, but it's just an Antec 500w power supply. My old one was a Raidmax, I don't know remember the watts but it came with a Raidmax...

Sorry for the non-specific title. I'll try and elaborate more here.

I went over the 'MY PC Won't Start' sticky, and did a search for other titles, but my problem seems to fall in-between...