Are you able to get into bios, if SO then:
Also, after you load defaults you need to go back into bios and change anything that deals with your HDD back to what it was orignally.
If you can not get into bios then:
Unplug PSU from wall, remove CMOS Battery, jumper the "clear CMOS" pins for 5 Min. Plug battery back in, wait another 10 Min then plug AC back for the PSU. Power on and see if you can get into bios.
As Col G said. Also, Daul bios on gigabyte boards are good for somethings.
If you have hosed the CMOS BIOS, normally requires RMA. Sometimes they have a utility that can recover from a bad flash, need to check the Asus Support formum.