The BIOS is a firmware program that resides in a programmable chip that is most often solderer to the motherboard.Write operations to firmware are allowed only in very specific conditions. There is a special sequence used to write anything to the firmware.
http://www.wikihow.com/Repair-Corrupted-BIOS-Firmware
The guy who wrote that is more goofy that I am. Do any motherboards now come with BIOS in a socket? If so, then all you need to do is buy a new BIOS chip and plug it in.
To answer his question directly; firmware is most often corrupted by an attempt to flash the firmware and the process does do work right. The possibility that a random software error could flash part of the BIOS is very remote.
Any environmental condition that would compromise the firmware chip would also endanger most of the other components. Heat, mechanical shock, static discharge. or cosmic rays can damage most components. A power surge bad enough to cook the BIOS would also take out the other support chips.
One other possible cause of premature BIOS chip failure is a manufacturing defeat that cause s one of more cells to lost is state, thus causing a binary 1 to become a 0, or the other way. One bit bit is enough to derail the program logic.
If the defect is persistent, flashing the firmware is of little value. Or maybe a temporary fix if it is a weak cell that only holds state for a limited time.
Again, if the chip is in a socket, the best choice is to replace the chip.
P.S. There are tools for programming a chip while it is in the board. That is way beyond the scope of this forum, IMHO. Instead, you send the motherboard back to the manufacturer to repair or replace the chip. At ate same time they can test the motherboard for any other issues.
