Try firstly clearing the CMOS (unplug the power cord and remove the CMOS battery for few minutes). Connect the monitor to the onboard.
If still the same, insert the motherboard's DVD and restart the PC. See if it does recover. If not, you can buy a BIOS chip fom ASUS eStore if in US or ebay (about 17$) and replace the board's one. It's on socket.