Well usually the computer will send a signal to which ever cable is plugged to your monitor, be it internal or discrete video, so you should check all connections and maybe try monitor on another system, if it works there then maybe your mobo is snafued,, hmmm. ???
Try resetting the bios. There is often a jumper to remove to do so that will be listed in the manual or look for the battery on the board, remove it for a few minutes and put it back in.