Black screen upon power up.

Hello,
When I press the power button on my pc. Everything run. But the screen stay black. Nothing come up. No letter, word, or arrow. A total black screen. I have test my monitor is work fine with other computer. Odd thing is my monitor power light keep blinking as like is not connected to anything. But the no signal box didn't come on. I have test the ram, graphic, card, and cpu. Is not it. Im thinking that is the hard drive or the mother board is gone. A black screen right at start up.