Unplug the power cord and remove the CMOS battery for few minutes. Unplug the graphics card and connect the monitor to the onboard. See if it does boot this way.
If still no go, you can try buying a BIOS chip and replacing the board's one. It's on socket.
I took out the battery and in the process had to take out my graphics card. Im still a little confused with the monitor part of this solution.