The Boot Block
The preceding section
discusses updating the program code in the system BIOS
by flashing it (replacing it under software
control). If the flash procedure is done improperly, the BIOS code can become corrupted, which will cause the system
to go into an unbootable state. Many newer systems come with a feature where a 4 KB "boot block" program is included as part of the BIOS. This is a tiny piece of code whose job it is to recover from a situation where the BIOS code is incorrect or corrupted.
If your motherboard
supports this feature, when the PC tries to boot and finds the BIOS code corrupted, the boot block will try to recover the BIOS code, usually by reading it from a specially-prepared floppy disk. You may have to change a jumper on the motherboard to enable this capability, and you may need to make use of a "plain vanilla" ISA video card. The boot block will load the BIOS code and then when you next reboot, the regular BIOS code should be in place and the problem resolved.
You will need to follow the special recovery procedure
outlined by your motherboard manufacturer if you want to take advantage of this feature.