Monitor no signal input

Hello,
I have 2 seperate computers that will not display a signal on the monitor. Both are desktops. 1 has an on-board video card and the other has a card. The one that has the card, I uninstalled and installed a new one, same thing. I have tried two different monitors on each computer and still no signal. However, I have tried both monitors on my laptop and they both work just fine. Anyone got any cause I got nothin!!!!

Thanks in advance.