My monitor cable wont work on the video card slot and keep saying "signal not found check cable" help!?

it work fine when i plug it into the on-board one, but wont work for my video card slot. used to work but all of a sudden saying that no signal check cable. and now i cant watch my shows on my big screen. anyone know why?|||You need to disable the onboard video. This can be done in the BIOS or by removing the jumper on the mobo for it.