as said before, yes, unfinalized sessions can sometimes do it, but there are a dozen other reasons just as likely such as:
- the computer just had a lapse during the intro or outro track burning, thus rendering the cd useless (but rescuable with software)
- the session wasn't finalized (but this is rare because most burning software makes it hard for you not to finalize it, and most computers will still read unfinalized cds nowadays)
- the CDFS FAT was written to a part of the disk that is physically defective, no fat, then you're in real deep shit, the FAT is like the DNA of the disk ... you can reconstruct it with software (because usually 99% of the FAT remains), but it's going to take till the cows come home again ...
these are the most common that i've seen ...
anyways, try recovery software like that one .... see if it helps