Ive had my home-built system for about 3 months now, and everything has been going great it runs perfect. But about 1 week ago it started every once in awhile to reboot multiple times until it would succeeding, I hit esc to get to bios but it only gives me 'boot first device', and will not let me get to Bios. Once it successfully boots it runs just like normal and performs great, with no reboots or freezes ever in windows. And it doesn't always reboot, it booted fine 3 days in a row then started rebooting again, I have not changed any settings in Bios or windows before this started. I have tried increasing my cpu voltage slightly, didn't seem to help,
I'm now going to repair windows.
Did you try adding a little voltage to RAM?
Run MemTest86 over night and check out your memory.
Does the problem still occur at stock CPU speed and with 1 video card installed?