Anything coming up on the screen at all? BIOS screen?
Did you check the video cable and monitor on another computer? If the monitor works OK, and you are using on-board video, you can try to find another video card to use to rule out an issue with only the video card. Or you'd have to replace the motherboard. You'd need to fix/replace something here, nothing you can do with no video output except replace the hardware that is not working.