A few years ago (2003-2005) I bought a Sony USB external DVD recorder for my Dell laptop and I used it to burn a lot of discs. Much later, when I tried to use one of these discs, I realised that I could not read it. The disc behaved as if it was scratched or dirty. I tried on a couple of different DVD drives but got the same effect. Sadly, all the discs that I burnt with that recorder suffer from the same problem.
Edit. When I read one of these discs with ImgBurn, I get lots of unrecovered read errors in multiple sectors, even at 1x speed. The sectors that cause read errors seem to be quite random; it's not always the same one.
I have no idea what could be wrong with the discs. I doubt that they are scratched or dirty; it would be too much of a coincidence that all the discs that I burnt with that recorder got damaged at the same time. Also, they don't show any physical defects. Is there any way to diagnose what the problem is and, hopefully, recover the contents of the discs?