Lost data problem

A friend of mine decided to install a clean WinXP when he greatly upgraded his primary PC and copied loads of stuff onto loads of DVDs. After formatting his hard drive and reinstalling Windows, he went on to put all the data back onto the hard drive that he needed. However, one of the discs was being detencted as a blank DVD by Windows and any applications which can use it.

It also did the same on his laptop and on his Fedora instalation on his other PC. There was a mark on the disc, so I cleaned it off (it was a fairly stubbern mark), and then tried the disc. Insteal of reading it as blank, it was now being noticed, but no data could be read off of it at all. So, Windows couldn’t even detect what kinda of DVD it was (audio, etc). The same happens with use of application and other OSs.

Seeings as the data is on that disc, I’m wondering whether or not it is possible for him to get it back. It had his SQL data on it (he’s still got his text files, but not his table info) and his Reason samples on it.

Does anybody know of a/several possible ways he could retrieve his data from the DVD onto his HDD?

Has he reinstalled Nero & INCD? It looks like the DVD might not have been closed so that any system without Nero/INCD could read it. I am rather guessing here.

As an aside if I were doing this I’d have at least 2 copies of important data, just in case.