So, I replaced the CPU, and finally got everything working. Was fine, stable, and I was happy. But then I had to fudge with the Overclocking controls of the mobo, and I did the following:
CPU voltage control: 1.35v
NB/HT-link voltage: +0.1v
FSB-Memory clock mode: Unlinked
CPU host frequency: 333mhz
Memory frequency: 800mhz
And from that point on - black screen. No beeps, nothing. CMOS clearning didn't help. Replacing a battery - didn't help. Disconnected the video, the HDs/DVDs, took out the CPU and memory - still no beeps. So - just the motherboard is connected now, with just the case pins and the PSU, nothing more. No beeps.
I highly doubt it has to do with the PSU, but I can check it with another PSU, just in case.
I was wondering - do you have any suggestion as to what I can do? What can it be? Any help would be appreciated, as I am truly clueless as to what to do next.
If you can't reset your motherboard even after having it all unplugged with no battery for an extended amount of time, it may be dead... possibly fried... but your settings were not extreme so a corrupted bios/cmos rom chip is a lot more likely.
If this is the case you could look for a rom chip to replace the one you have (has to be working from same model mobo) or get a programming tool and re-flash the bios to the chip. in some cases if the bios chip is soldered onto the board it will be a harder thing to accomplish.
So your last option is to look for another 775 motherboard... possibly with a better chipset. Intel would be way better than nVidia's nforce. You can find some pretty nice 775 boards on ebay and other sites...