Lost all Video to Monitor - existing build

[probe47]

I have a Window 7 box that will not display on the monitor. This is a box that has worked for a long time. Switched out the video card (PCI express) for a new one still no video. Switched monitors, still no display, installed an old PCI card and still no display. I get nothing when I turn the box on except for the fans starting and the lights on the motherboard. Any suggestions or thoughts I would appreciate. Since I cannot see anything on the monitor, it is hard to diagnose.

 

[Tmagic650]

This is a box that has worked for a long time... the motherboard may have died, even with the fans and lights