Do you have the correct connection to the video card from the power supply? I would also try the breadboard test out of the case using onboard video. For beep codes, connect the front case speaker if yours has one. Breadboarding is a generic term for testing the board on any non conductive surface such as wood or cardboard.
It's the 24-pin ATX power connector on the motherboard beside your RAM on the right edge of the motherboard. Also, make sure you have the 4-pin CPU power connector connected, it's beside your VGA and DVI ports in the top left corner of the motherboard.
what is the 12v connector specifically? Does it connect to the motherboard, the video card?
It those basic checkpoints for hardware configuration don't fix the problem, you can unplug all power connection and reconnect them after hours .. just try to get into bios, check the bios version and give it the latest update, if it is some cold boot issue, it should be known with solution.
i had another psu in my room from my friend, not a full pc.
Anyways, i decided to just send the motherboard back for replacement after the same thing happened with just the mobo, the psu, and the cpu/fan together. Hopefully it's not the cpu that is broken, but i didn't have anything to test with.