Friend's computer not booting up

[PCFetish]

My friend have a problem with his computer.
Power comes on, fans running hard drive turnning but nothing on the screen.
It's not video card. I swapped with my vide card and it still does nothing
I tried my PSU and still nothing.
Tried different ram, no difference
There is no beep at start
He's computer is not overclocked
Funny thing is that he tells me that it sometimes works, after some kicking and punching
What's could be causing this?

 

[newbiepcuser]

Maybe the motherboard isn't mounted securely and its shorting itself out. Did you remount the cpu?

 

[MDE]

Try running it with the motherboard outside of the case to see if the mobo is shorting out on the case.