Xfx 750w possibly gone bad!

Just put a system together with the following parts:
Xfx 750w
Asus gtx 560ti
Asus sabertooth p67
Intel i5 2500K

When the computer is in sleep mode and I press the power button on the case, it shuts down before it restarts.
Occasionally when I turn on the computer the power supply shuts down in a matter of seconds. Then it powers itself back up and it stays on, however nothing is being shown on screen. So I have to turn it off manually before i turn it on again.
What do you guys think?

Could be a bad mobo too...

Do u have a spare psu to test it with? My money's on the psu. Also I'd try rebuilding the entire pc just to make sure every thing was connected properly.

if i have read what you are saying correctally, then it sounds more like the doubble boot thing of the motherboard, and motherboard bios, not the power supply.
doubble boots are just the motherboard checking testing stuff before , it is usually nothing to worry about.
if you set everything on standard, or Default the whole bios, does it do it? usually the doubble boot action is a safety action , used in Nonstandard settings. Just like your not sure if a non-standard setting will work, the motherboard isnt sure either

then
the blank screen, it comming up with no video, is often the video failing on init, could be due to a slightly too high of overclock, bad negotition of the links on init, or it indeed could be a power issue.

so as usual it could be many things. if it doesnt do it on standard settings, that give you more clues.
check for any updates to the motherboard firmware bios.
.

Rebuilt the system and updated the bios, it seems to be working fine now!
Thanks guys!

Spoke too soon guys, same problems as before. By the way, its highly likely that its not the mobo since I tested it with another motherboard.
Another thing that really scared me was when I was trying to reach 5 ghz i set the voltage in asus aisuite II to 1,4 volts when it suddenly bumped up to 1,6! The temps skyrocketed up to about 98 degrees in a matter of milliseconds. ( By the way, I always use the bios for overclocking, this was an exeption).
Do you think this was a software bug or a hardware problem.

If it requires a retry to boot the PC cold, then please enable load line calibration for the cores.
(At least with Intel, can't confirm with AMD, ATM.)

I found that it will give me a hard time on a cold boot if I don't enable load line calibration!
(It will act like my weedwhacker!)

Booting the pc after it has been shut of for a while is actually not a problem. Restarting it and such, is.