Do you have the manual?
Don't use that board, but the P4P800 manual gives full instructions for the 800. It uses a utility called afudos to backup the BIOS to floppy in DOS. You might also be able to recover your BIOS by booting from the support CD ROM. It should detect a corrupt BIOS and lead you through the recovery.
Suspect it is the same for your board.
If you go here
you may be able to download the manual for your board. It's about 7mb, but I could not get it to download. You might like to try.
Regards Brian j