I've seen such things when two different video cards were left enabled in Device Manager.. Access the onboard graphics device in Device Manager and select "Disable this device" at the bottom.
If such has already been done, then I'll agree. It sounds like it's time for a new motherboard.
Hope this helps.
A customer brought in a Compaq Presario S6220WM that wouldn't even finish booting before the video died. The power stayed on, but the monitor lost any signal. If you tried to boot into Safe Mode, or installed a PCI video card, the same thing would happen. (We configured the BIOS for PCI video before installing the PCI card.) We reset the configuration settings in BIOS, and the computer now at least makes it to the desktop for several minutes before the video dies. As I say, the video dies even in Safe Mode, or with a PCI video card installed. We're puzzled, and can only figure a mobo failure. Any ideas?