PC only starting for 1 second

[Jackr987]

hello im re-assembling my brothers PC, i put everything together and when i hit the power button the pc will sometimes start up for only 1 second and then power down. I have tried connecting it to another psu and case but the PC just wont start for more than a sec. any help would be very appreciated!
thanks

 

[alexoiu]

It looks like a short. Have you used standoffs for installing the motherboard? Make sure that each one matches a board screw hole.