I have Sony DDU1621 DVD-rom and flashed it with 4.2 firmware , first was with 1.5s and now bios can not find it and i do not know how to return the old one because dvd is not detectable . Another problem is with Yamaha CRW2100E . It stops reads and burns CD-RW only cd-r I flashed it with 1.0n but the problem remains . Please help me .
S1.7 and not 4.2 were the correct firmware for your drive!Maybe you can rescue your drive using mtkflash (in true DOS), no idea if that will work.
In case of your Yamaha: Clean it using a lens cleaner.
I try in real dos but when bios can not detect it dos can not find it too . About yamaha i clean it but no efekt .
Some good DOS flashers doesn't need a drive detected prior by the BIOS.Mtkflash would be such one, but chances are slim that Mtkflash would work with your drive.
This is the program i used and it can not find my dvd .