MA78GPM-DS2H NOT WORKING WITH NEW PSU

[nicklass]

Hi
I bought a new 750 watt gaming psu and it will not boot my mobo properly, it will boot to BIOS but after a while the usb becomes non responsive or not work at all in bios.
I have gone into bios with the old psu installed and made sure USB is enabled in the bios and put the new psu back in and still usb keyboard non responsive in bios.
I have tested the new psu in another computer and it works fine and i have tried another gaming psu and it has the same problem screwing up the usb when booting in to bios.
The bios version is F5 the latest.
Any idear peoples.??

[Vezina]

Please post the full configuration and the specify the brand of the power supply and the amount of Ampers on the 12V rail.

There is no such thing as "gaming PSU" there are good PSU-s and and crappy ones no matter the amount of watts you see on the label.

Check if you inserted all the connectors into the mobo.

Keep in mind that a basic config doesnt need more than 400-450 "real" watts ,using a 750W one will lead to a very low load most of the time meaning more power consumption from the grid as the maximum  efficiency is obtained for a power supply somewhere in between 30%-75% load.