Double-check that the problem isn't merely that your DVD is dirty. Even the smallest bit of dust can make a DVD unable to play. Use a soft cloth to carefully wipe down the disc and remove any dirt that might be creating problems.
Visually inspect the disc--if you can see a scratch or another mark that needs to be fixed, you have found the problem. If the scratch is vertical, going from the inner part of the disc to the outer part, it will be simpler to fix than if it runs along the circular pattern of the disc.
Use toothpaste to clean the disc--this solution has worked for many people. Toothpaste removes extra plastic from the area that is scratched and lessens the effect of the scratch. However, be careful with this method, as toothpaste can cause more problems if not used correctly.
Look into buying or borrowing a disc refinisher. There are many products available such as Disc Doctor which can fix scratches or marks on your DVD. Such products will come with easy-to-follow instructions. However, you may have to use the product more than once before your disc is fully repaired.
Wax the disc. If none of the above steps works, try using petroleum jelly. If the disc does start working again with this method, though, know that it is a temporary fix and you should make a copy of the disc as soon as possible.
