My system specs:
Intel DX58SO motherboard
6GB (3 x 2GB) Corsair memory
nVidia Quadro FX 1800
1TB seagate HD
When I power the computer on, it goes to the "Starting Windows" screen (with the Windows logo), then it abruptly shuts down, and then powers on again. Then it gives me a choice: "Launch Startup Repair" or "Start Windows Normally". If I choose to start normally, it restarts itself at the logo screen. If I choose repair, it loads files, but restarts once it gets to the logo screen.
I can hit F8 before the logo screen to enter safe mode. I ran AVG and Malware, which got rid of a couple of viruses. I ran memtest and a HD diagnostic, and they both check out OK.
I don't have a system image to recover to. And I backed up my important files, and tried to reinstall windows, but the same thing happens: I boot from the disc, it says "Windows is loading files," then it says "Starting Windows," and it restarts all over again.
frankly i'm stumped. It's not the drives or the memory. Its not the PSU, because I have a spare and tried both. I tried 2 different GPUs. And I can run safe mode, so I shouldnt be concerned about the motherboard or cpu?
I think we have just a few tries left.
Start the PC in safe mode and try to uninstall the Nvidia drivers completely.
Then let the rig reboot and see if it get's into windows normally.
I'd also suggest removing all the RAM except one stick and try the above stuff.
Although you already mentioned that there is nothing wrong with either the drivers or the RAM, I'd still suggest you do that.