Desktop - no video, sound, or keyboard lights

I'm normally the guy who fixes peoples computer (not professional, just hobbiest), but this issue is a little elusive.

Normally if their is a simple hardware working issue I would hear beeps or the computer would POST, then complain. In this case, I get no sounds, or video, and not even the keyboard lights turn on, HOWEVER the computer is powered on, and the fans are running.

I've already tried reseating all power cables in the case, and that allowed my computer to turn on for 30 minutes, then it shutdown unexpectedly and wouldn't fully turn on again.

I'm going to try using a different GPU (8800gtx) and take out all but one stick of ram, but I don't think either will make a difference.
That is the extend of the hardware I can switch out. If this doesn't work I'm thinking of buying a power supply just to see if that will solve the issue.

System:
q6600
EP43 UD3L
4gb Patriot
Sparkle gt 470
OCZ 700w PSU

I'm looking for both suggestions for troubleshooting and estimates as to what the issue could be. My guess is the power supply.

Reply 1 : Desktop - no video, sound, or keyboard lights

I did try replacing the GPU and that didn't solve it.
Tomorrow I will contact local suppliers and try and get my hands on a temp GPU.

Reply 2 : Desktop - no video, sound, or keyboard lights

I had an unit like that. It turned out that someone unplugged the ATX12V connector.

Fans and such worked, but no blink on the keyboard or much else.
Bob

Reply 3 : Desktop - no video, sound, or keyboard lights

If so, I think your hypothesis may be correct.
When I was trying to get it to work earlier, I reseated all of the power cables including that one, and it turned on for a while, before failing again.

Further my PSU is annoying and actually seperates that 24 pin connector into two parts, both plug into the same plug: 20 pins on the left and 4 pins on the right. Is this normal? It sounds like a bad design.

Reply 4 : Desktop - no video, sound, or keyboard lights

http://i175.photobucket.com/albums/w146/rproffitt2000/EP43.jpg

Reply 5 : Desktop - no video, sound, or keyboard lights

I admit I didn't replug the processor power plug. It is under a huge power sink, so in order to replug it in I have to remove the heatsink and reattach it.

Still, I should try this. I'll do it tomorrow when I'm less inebriated. Thanks for the suggestion.
Also as an update, I didn't get around to getting a PSU today, and I'll have to wait till after easter Monday, because everywhere is closed. Thanks a lot for the help thus far. I'll update on Tuesday. Again, thanks.

Reply 6 : Desktop - no video, sound, or keyboard lights

Ok I am quite sure that this is a motherboard related issue. The MB needs to be fixed. After some point of time the capacitors becomes week and that result in the above situation. Again there can be 1000's of more reason for your problem but this one come first in my list