Actually Sony only offers the DSxx firmwares. The DH12 is offered by HP, the D803 by Lenovo and the DX14 by Gateway.
If a drive suddenly stops working, that has absolutely nothing to do with its firmware. It is either a computer software problem or a drive hardware problem, not a firmware problem.
Based on what you've done already I would guess it is not a computer software problem, which leaves us with a likely hardware problem.
Either the lens got dirty over time or the laser degraded/died. Try cleaning the lens. If that doesn't work, then your drive is dead, so you'll have to buy a replacement drive ... and choose wisely ... the last thing you want is to get another poor quality QSI clone, a Teac or heavens forbid, a Matshita/Panasonic ...
Choose a newer IDE drive which has good firmware support and one which is well supported by third party tools on this forum. You can find plenty of cheap alternatives on eBay, if you don't want to pay over the odds for a 'retail' replacement.