Computer boots up but monitor says 'no video signal'?

[TYLERisMiSfIt]

so my friend needs help when he starts up his computer the screen does not display anything but he can hear everything going on in the background, could it be a GPU problem or Mobo problem?

 

[RastislavB]

Can he try a different video output? If he's using one on the GPU can he try the one on the motherboard?