This is most likely a lens problem.
I don't think it could be anything else as like you said, you've already installed a host of different firmwares and it has had no effect on your problem.
I think that the DVD part of the lens in the drive may have died, it is possible after all. There are usually two parts of a lens in most drives - one for CDs and one for DVDs. If only one reads and burns, then the other is faulty.
Have you tried using a DVD Lens Cleaner in this drive? Or tried opening up the drive and cleaning the lens physically? It could help.
I think that this is all you have left to do. You could try carrying out a fresh install of Windows if you want but I suspect that it will not solve your problem.