Computer wont start up

My computer shut down with no warning while I was asleep(woke me up...its kinda loud with 5 fans and when it shuts down there is a noticable change in sound in my room). I had just been using it 3 hours earlier with no problems. Now it wont turn on. It appears as if everything is getting power. My fans all light up and/or spin up, my cd drive still ejects disks(if I unplug the IDE cable...it wont if I leave it in), my hard drive cooler displays the temp and spins up. My USB hub even lights up as does the light on my built in LAN card. The CPU cooler also spins up so it looks like everything is getting power. However the computer itself wont POST or anything. Everything spins up, but I dont get any video, no bios, nothing. One last interesting facet to note:my keyboard is not receiving power, or atleast doesnt appear to be but that might be because it doesnt boot-up at all.

Could it be my motherboard that fried and caused the sudden shut down? I am hoping its not PSU related.(I wouldnt think so if everything else turns on atleast). Since it isnt posting that leads me to think its a bad mobo instead of a bad PSU. Would a bad motherboard cause the whole system to turn off though?

I have an old offbrand NF4 Ultra socket 939 motherboard
AMD 3700+
1 gb DDR400
Nvidia 8800 GTS
2 internal IDE HDDs
1 DVDRW
850W/62A Thermaltake Toughpower PSU

I was planning to upgrade in January to a 790FX/PhenomII 955 BE based system(all new build - except PSU, I was planning on keeping that) just hadnt scrapped the cash together yet.

So what do you think? Bad Mobo? Any help would be appreciated.

I just pulled all the ram...I dont get any beeps like I know I should.

When you say you pulled the ram, do you mean you took them out and replaced them with known working ones or just pulled them out?

What brand is the motherboard?

I would try an out of the case setup. Set the board on some sort of cardboard and only hook up basic/minimal components.