Dell Dimension L866r hangs after POST after BIOS flash

"Try to boot your board into emergency maintenance mode (usually known as Boot Block Recovery). In this mode the BIOS will only boot a minimal floppy disk boot block. This boot block will boot and run a floppy, and provides no keyboard input or screen output. So the restore process has to work completely automated. You will need a backup of your old BIOS of course and a prepared boot floppy with flash program and some automation code in an AUTOEXEC.BAT. To enter this mode, usually some obscure key combinations are to be held down during power-on, or an onboard-jumper needs to be set.

Another approach could be to find an electronic retailer and ask him to flash your BIOS chip with the backup image (you'll need to give that to him, too). Either take your complete motherboard there or CAREFULLY remove the BIOS chip yourself and take that to the retailer. Most electronic retailers are able to reflash these chips with special flashing devices.

PS: Boot Block Recovery probably won't work if the update overwrote the boot block or if that part of the BIOS wasn't write protected. Usually one cannot overwrite the boot block."