Gigabyte GA-X79-UD3 do not boot

[F9V]

Hi everyone,
I write you because I do not know how to solve a problem with my motherboard.
I bought the new pieces, assembled them and try to turn on the computer, spend 5-6 seconds and everything is shut down, then reboot again and then go off to infinity again (I think).
I tried to start only mounting the motherboard without cpu, ram and more, attacking power 24 pin and 4 +4 pin, but it does not start. So i think it's a problem of the motherboard...

The hardware I've installed:
MB: Gigabyte GA-x79-UD3
CPU: Intel LGA2011 Xeon E5 2603
RAM: 4x8gb Geil Stroke GOC332GB1600C10QC
PSU: Cooler Master GX 750w
HD: Corsair forice 60gbx4 + 1tb wd10ears
VGA: Radeon 5970
CASE: Silver Katana
CPU Cooler: Noctua NH-U9B SE2 + I2011-KIT NM

I tried to start it out of the case and mount it with only the ram in slot 1 + cpu + cpu cooler, but will not start. If you think that the cause is the power I say no right away because until recently it worked with my old LGA1366 platform (and even now if I try to start it with my old motherboard, ASUS P6T SE, works perfectly) ...

PS: Sorry for my bad english

[ex58]

I think that BIOS installed on your UD3 did not support Xeon CPU,which is supported from F9 and above.
http://www.gigabyte.com/support-downloads/cpu-support-popup.aspx?pid=4050

Try to borrow any Core i7 CPU ,just to flash to latest BIOS.

[F9V]

Ok but.. Why If I start the pc without CPU, turn off anyway? My Asus P6T SE remains on when I turn on without the cpu ...

[jaykay2]

OK mine is sorted!! WooHoo

You have to connect the TWO 12v ATX connectors from the PSU to the socket on the mobo, connecting the 24 pin main mobo power connector is not enough!

Page 23 of the motherboard manual (english) says "if the 12v power connector is not connected, the computer will not start"

Worked for me, hope it helps anyone else reading this. I cannot believe I dod not connect them!