Data corruption on optical media is a common problem due to physical damage to the media like scratches, surprisingly data can still be recovered from non-readable scratched sectors on CD and DVD's using the following method.
A CD/DVD reader uses a laser beam to read the data on the disk. This laser beam crosses the protective plastic layer and reads the real recording metal layer. If the protective plastic layer is scratched, the laser will be unable to pass resulting in non-readable disc.
If somehow we manage to re-smooth this protective layer then the laser will reach the data and read it, now there are many ways we can achieve this using common household items as written below:
1). Toothpaste - Yups! toothpaste, you can use any non-gel based toothpaste for this, just put a very small amount of it on the scratched area and polish it gently using a cotton swab, sometimes the paste may cause new minor scratches but they are just superficial. Now just wash the cd using water.
2). If the above trick does not work try some metal polish like Brasso gently wiping with a soft cotton ball followed by application of Vaseline.
3). Baking Soda - make a small quantity of baking soda paste and apply using a soft cotton cloth buffing the bad scratch. Clean the baking soda before using the disc.
4). You can also try using some oil as a polishing agent this also works many times.
There could be many more daily use products which can be used to fix scratched CD/DVD media and get them working, just keep on experimenting.