Reflash Supermicro BIOS Chip with external EEPROM programmer
You don't say what kind of Supermicro motherboard it is, or how old. Some motherboards have a last-ditch failsafe BIOS update method; often it involves hooking up a floppy drive, putting in a disk with the new BIOS, and then setting a jumper or hitting a key combination on power-up. That may be your best bet, if it's available.
On Sun workstations we used to deal with this type of problem by installing a known-good chip, booting the machine, then pulling the chip with the power on and socketing in the bad one for reprogramming. Obviously this is a super scary procedure. There are a lot of risks and you can end up frying the chip, the motherboard, or both. I've never tried it on a PC, so I can't recommend it with a clear conscience. I will say I did about half a dozen Sparcstation SLCs and they all survived, though.