ASUS motherboard turns off after bootup

my pc motherboard Asus P5GL-MX will bootup go to windows login screen or setup and just turn itself off randomly could stay powered on for 12 seconds next time 20 seconds sometimes 5 seconds but it switches off , power supply is good it was used well on other motherboard , what could be the problem ?

 

grounding problem ??

I've heard something like this could be related to the motherboard either not being grounded properly or being grounded to the case (whatever that means) in fact i'm beyond my knowledge here so disregard my post and wait for an expert.

 

My first guess would be the power supply or bad motherboard but it's unlikely it's the motherboard as it works. It could also be a loose cable or something shorting out. Do you have another power supply?

 

well i was testing out the motherboard on a table not in the case, I'll check the cpu heatsink as well and let you know. POWER supply is good it works with other motherboards so is the cabling !

 

Are you getting any BIOS beeps at all?