Installed a new GPU, and PC won't boot. Turn it on and:

• No monitor signal at all (tried HDMI and VGA via DVI, on 2 working monitors).
• CPU and GPU fans DO spin, but
• No system beeps, no sounds from drives (they might make a small noise in the first 1 second or so, but there's definitely no OS loading or anything like that)
• If hit "power off" button it turns off immediately (no holding down for 3 seconds like usual)

If I put my old HD 5670 GPU back in, everything works fine.

But (plot twist!) card is not totally dead. My friend put it in his PC, and it works fine (he even played a game for 15 minutes, no issues). He has a Corsair TX850 850W and a Gigabyte MB.

So my main theory is: the GPU isn't getting enough power from the PSU. But is it:

• Bad PSU? Seems unlikely, since it works fine with the other GPU. Also, the PSU Is brand new and 550W (single 42A/504W 12V rail). Overkill for this GPU. Corsair is a decent brand, but maybe just mine is faulty?

• Bad GPU? Could it be drawing more power than it should be, somehow, or something? Supposedly HD 7790 needs only 21A/75W on the 12v rail, though this one is factory overclocked a bit... but should that triple the power requirement?

• Something else? Could there be a motherboard incompatibility somehow? Both MB and GPU are less than a year old and PCI Express 3.0 x16.

Things I've tried:

• Re-seating the video card
• Testing PC with old GPU (works fine, same PCIe slot).
• Checked AMD's stated amp/watt requirements of a 7790 and my PSU (see above). My PSU can output twice the amps (single rail) and 5x the Wattage a 7790 needs.

Here are the full specs:

Gigabyte HD 7790 1GB OC GPU
Corsair VS550 550W PSU
4GB RAM
AsRock H61M U3S3 motherboard
i3-2100
500GB SATA HDD (2007-ish)
blu-ray drive (new)
PCI 802.11g card

Edit: Motherboard BIOS Update seems to have fixed it. (If anyone has same problem and it doesn't work, comment here).