Bad media, bad burn or a combination of the two. Despite the claims of DVDs lasting decades, yours is 14 years old and possibly just going/gone bad. Which is why it's critical to copy your discs and data on other media (hard drives, tape, etc) to new media every few years.
Try a different reader and/or different machines. If it's still not recognized, try using
ISO Buster and ISO Puzzle. You'll have to buy to full program to complete the recovery, but it do enough to let you know if it's able to recover anything or not.
Standalone DVD players are far more tolerant about playing marginally DVDs because they're single function, unlike PC DVD readers/writers.
Also, are you sure the disc has something written to it? You can tell because the underside will be a lighter purple/blue where the data's written. Sometimes we just forget that we never used that disc!