Hi there Elder!
I have found that many DVD players are more sensitive to scratches than others, even if there's a very fine scratch or fingerprint, the laser can be interrupted. Also check that the reverse (label) side of the disc isn't scratched too. However you state that it is not scratched, this becomes a more interesting issue.
- Be sure the DVD is a genuine GDI product.
- Check if the DVD player is Region Free (Multi-Region).
- In Windows XP, make sure that Windows Media Player 9 or later is installed.
- You may need to install a 'DVD Decoder Plug-in' on Windows XP for the DVD to play.
Apart from that, I feel it may be a bit of a mystery! Good luck!