I will try to be as explicit in details so you guys have as much to go on as possible.

The basic problem is this.

I built a pretty amazing machine six months ago (hardware is shown at the end of this post). It has been running pretty well. I have several fans installed to cool things down as well as heat pipes on the mobo, but I noticed through the summer that it seemed to get hot and occasionally shut down after running for several days (this would happen OCCASIONALLY - NOT CONSISTENTLY and after letting it cool off for a few minutes it would start up without issue).

The other night it shut off. Now when I start it up the following happens. Power supply turns on and seems to be supplying power to everything (all fans are working). I do not get a POST (I get no signal to the monitor at all) and I do not get any diagnostic beeps.

I have tried the following with no change in result:
I disconnected the hard drives.
I reset CMOS.
I have pulled the RAM and reseated.
I pulled the video card and reseated.

My guess is that something blew, due to heat buildup (strange thing is that I really don't think it was running that hot because the temperature has cooled off considerably), but without any diagnostics I don't really know where to start.

Any help would be much appreciated.

System Specs:
Gigabyte N680SLI-DQ6 Mobo
Intel Core 2 Duo 3MHz
EVGA e-GeForce 8800GTS
4x1GB Corsair Dominator
Coolmax CTG-1000 1000W Power Supply
5 Seagate SATA Harddrives

I seem to be facing the same problem. Almost on similar grounds. Of course, I am not running a configuration as high as you are. I am on an Intel DG965RY mobo & am using a Chieftec 350W Power Supply.

Were you able to find a solution to your problem? If yes, what did you do?

does your heatsink got enough thermal compound on it? it could be a overheating problem..i encountered the same problem my computer keeps on restarting only to find out that my processor was faulty..but you need to double check there are a lot of causes for such problem, i supposed your devices are still under warranty as you said you just bought it six months ago, take it back to the dealer and request to change the parts

This combo is able to report CPU temperatures, I believe. have you looked into this so that cguan_77's theory can be checked out?

Thanks for all the replies till now. You guys helped a lot! My problem was detected... This was a faulty motherboard!

Also, I learnt one more, which I was not aware of... If you have RAM's of different frequencies, your machine is bound to reboot and give you strange behaviour! I have witnessed this!!

Looks like it was a bad stick of ram...