Use dosflash16 to erase the drive first then write the new firmware. If no joy, erase the firmware again using dosflash16 and then completely restart dosflash and write the correct firmware, keep your fingers crossed.
You need to clear out the bad firmware first, it doesnt matter if dosflash doesnt recognize the drive properly, just erase it as no firmware is better than the state it is in at the moment amoungst other reasons I do not have time to explain.