Hi
If you have access to another PC with a DVD writer
Try copying the faulty DVD to a good quality branded DVD-r..
Also setting slow copy speed say 4 or 8 not 12 or 16 etc
If you get no error messages during copying this may work.
Software such as ImgBurn,(free) & many more CD/DVD software will copy DVDs
(But do not use the latest ImgBurn version 2.5.8 due to included adware in the installer use 2.5.7)
regards
Mike Barnes