Custom build not starting

[SebHolmes]

Hello,
My custom build pc, won't start, it turn on and all the fans spin, but then turns off after 5 seconds.
What could be the problem?

 

[maestro0428]

List your full specs please. Also, check that all of the plugs and parts a fully seated into the motherboard.

 

[13thmonkey]

have you used stand off between the mobo and tray?