I agree with the last guy. I would reseat the video card if you have a pci express card as opposed to on board. One other thing, does the BIOS pop up on the screen when you bootup and then you loose display when it gets to windows, or is there no display at all?
If the monitor works on another machine, I would say it's definitely not the monitor. Once you reseat the video card, if the display still does not come on. You may have a faulty video card. Good luck!