Try resetting the CMOS, this will re-set the BIOS to its default values - hopefully enabling your on-board video.
Disconnect the power cord. Ground yourself. Look in the lower left-hand corner of the board. Find the CLR_CMOS (Clearing CMOS Jumper) - two pins (page 30 of the manual
). Use this jumper to clear the CMOS values (e.g. date information and BIOS configurations) and reset the CMOS values to factory defaults. To clear the CMOS values, place a jumper cap on the two pins to temporarily short the two pins or use a metal object like a screwdriver to touch the two pins for a few seconds. Connect the power cord. Push the power button. Press the <delete> while the computer is posting to access the BIOS.
If you still have no video during POST, move the video cord to the other output and try again.