I have hotflashed a lot of biosses on a simple 430TX board, including Asus p2b/p3b series and p5a and p5a/b bios.

Try using uniflash , worked for me every time. Boot from a floppy that holds the p3b-f bios and uniflash.exe and after booting dos simply replace the chip. After that you can start uniflash. So no swapping after starting uniflash.

Thanks for reply. Still no joy with uniflash. I tried backing up the p2b bios from its own chip and flashing it to the p3b chip to prove the chip was ok, rebooted fine so proves chip working.
Then reflashed the both p3b backup i had made and the downloaded bios from asus, both times the p3b board starts but puts out no vga signal or does anything further.

Board dead?