I have (and have for over a year now) a system which has been running fine until now as it's just decided to stop POSTing. The setup consists of:
Gigabyte GA-MA790FX-DQ6 motherboard
AMX Phenom X4 9950 CPU
Patriot 1066 2 x 2GB (4GB)
Corsair TX650W Power supply
Everything else in the case is irrelavent now as I've disconnected everything other than those listed above.
I've also tried shorting the CMOS pins/removing the battery.
The BIOS was at the latest revision F7B (and had been since the update was released) and no problems experienced there.
I get no POST beep / no display when the Nvidia 8600 is connected.
When connecting the HDD the LED seems to stay on constant.
When connecting the DVD the LED flashes at approx 1s intervals and the drive makes a sound like it's about to read.
Nothing in the system has been changed since the original build.
Went through a few more checks, seems it's the power supply. Took the existing Corsair TX650W out (which seems to power everything up) and placed in one from another machine, it booted fine, put the suspected faulty one in the machine that I just took the working one out of, that won't boot either. Strange that it powers fans, HDD, DVD and everything but doesn't give enough to POST.
Done voltage checks and everything seems to be correct on all the moxel/4pin/24pin connections.. Requested RMA from Corsair as it's 5yr warranty.
When power supplies fail, they *could* still load windows. My work computer's PS went up in a puff of smoke, which I though was amusing, and then restarted. I got to the desktop after the restart, but when I opened any programs from Office, it restarted itself again.
So, it running fans and stuff seems like easy business. Glad you got it sorted.