Is it an onboard video? and does it have an AGP or PCIe slot for a upgrade video card.

If that is the case, then enter the BIOS (set up) and make sure that the correct bus is enabled for the graphics.....will be the following options:
Graphics controller or close to this as each mobo uses a different wording!

ON Board or PCI
AGP
PCIe

You are using on-board graphics then the correct selection has to be On-Board or PCI

if it is enabled for something else then your graphics will not work.