What BIOS flasher and application to flash are you using, as normally it would work. Also what error is the flashing application giving you? By the way, what is the BIOS chip's part number?
I would also try to download the A10 version of the BIOS and flash with that as the A12 tends to break computers every now and then.
Also if the BIOS chip is fine, instructions below will most likely work (Got them from DELL):
1. Download the Dell BIOS update .exe file to a USB flash drive.
2. Run the .exe file with /writehdrfile parameter
3. Run the .exe file with /writeromfile parameter
4. Copy the .hdr file to winery50.hdr
5. Remove the battery and AC power from the dead computer
6. Insert the flash drive into the dead computer's USB port
7. Hold down the End key and then connect the AC power
8. Dead computer reads USB flash and asks if update should be done
9. Allow the update to finish and then reboot.
10. Computer is now working normally.