Ok guys, I'm seriously getting angry and I can't cuss on these forums.
I got my new Antec TruePower2.0 550W PSU today, and dropped it in my case. Connected the 24-pin thing to the 24-pin power slot on my motherboard. Connected a PCI-E power connector to my PCI-E 7900GT. Connected 2 of the SATA power connectors to my 2x SATA harddrives.Connected a 4-prong molex connector to my DVD+RW drive. Connected the little floppy power connector to my floppy drive. Plugged in the thing that powers my case's from fans, power button, etc. Had an 8-pin thing coming out of the motherboard I didn't know what to do with until I discovered it split into 2x 4-pin connectors, so I connected the one that fit to my motherboard's ATX12V thing in the top left corner near the PSU. Plugged it in, hoped it would work. Nothing. The fans/LEDs/etc in my case came on, I could see my CPU fan going, I could feel my harddrives going, I could even feel my video card fan running, as far as I could tell. Yet when the monitor went from orange light to green light, it said "Off Mode in 5 sec" and then proceeds to go back to orange light mode. I don't have the SLIGHTEST idea what could be wrong here. Was my first 7900GT even DOA, or had I done something wrong. If it was DOA, is there the slight chance that this one could have been DOA also?
I'm at an utter loss here. Please, ask me as many questions as necessary to make it possible to narrow down what the problem could be.