I'm in need some major help, please! :(

About oh, two weeks or so ago, my computer flatlined on me, it wouldn't boot at all, no beeps, nothing. After some hard work and tinkering I believed at the time my problem was coming from my motherboard and or CPU. I spent a good day toiling over parts checking the thing in and out to see what could be the problem, to this day I have yet to truly figure out what it was. With the new parts I bought for it, it seemed to work (MOBO,CPU,RAM), but even then that felt like a patch work solution to a problem that was bigger than I thought.

Computer specs before and after - parts in bold are the new ones.
Asus P5N32 SLI SE Deluxe /Asus P5Q
E6600 @ 2.88 Ghz /E8400 @ 3.00 Ghz
Corsair XMS2 2Gb @ 800Mhz /Corsair XMS2 4Gb (2 sticks) @ 1066Mhz
GF 8800 GTS 640Mb
OCZ 850W PSU
WD Caviar II 250Gb & 320Gb

Previously I had been overclocking my old setup, I had a few overvolt failures, but those were more closer to the day my computer flatlined on me. Previously I had a 600W OCZ PSU, and to my recollection I don't believe I ever had that happen to me, and even if it did it was once or twice at all. Cue in today, when my computer randomly goes into sleep mode - or so I think - I attempt to get it go back but it doesn't so I restart. Much to my dismay it doesn't boot up again, this time I get three beeps, one semi long one, and two quick short ones. I then attempt to restart again and my computer flatlines out on me. I don't know how else to put it, but here are some of the things I noticed:

-Computer will boot if I switch the video card, I'm running on a 7100GS at as we speak.

-At first I attempted to get all of the stuff from my HDD before I did a clean reformat, but mistakenly I didn't have the proper drivers for my new motherboard, so that didn't turn out all that well. I attempted to boot up my computer again and then it flatlined on me.

-At the time, by unplugging the six pin plug from the video card, turning on the computer and hearing it give me that long beep as in it saying that there was no video card - I can only guess it to be that - and then turning it off; plugging it back and turning on my computer would sometimes get it boot up. Also sometimes even switching the six pin connector that I was using would work as well.

-My patchwork solution was this http://www.yinfor.com/blog/archives/images/4pin_to_6pin.jpg. For the past two weeks it has seemingly worked and gotten it to boot up, but now even that wont work.

-When I turn off my computer from Vista, the operating system will shut down but the computer itself wont.

-I've checked to make sure all of my PSU connectors are in place, and I'm beginning to think that is exactly my problem. The only thing I probably don't have connected is that optional 8 pin because my PSU doesn't have the appropriate plug, I've only got it half, as in the 4 pin.

So what's your take guys? I can RMA my PSU since it's fairly new, almost half a year, but then again I still wouldn't know the problem. I was fairly confident that it was my a problem associated with the parts I replaced, but now I'm afraid at pointing the finger at anything. It runs fine with the card I have in it right now, but the card itself is not as demanding as a 8800 GTS. I'm tempted to keep my system like this for a little while longer to see if anything continues to happen, but I also use my PC to game and well it's a giant bummer. I think I might end up having to buy a PSU tester to check it out as well.