How to repair a CD or DVD of any kind.

READ this first!!!!!! Seriously ... important

Repair directions.
Soiling, scratches or scuffs are probably the cause of your problems with media not reading and causing skips or keeping a CD from playing.
Basic and simple "cleaning" can be done with tepid water and a mild detergent but our Protect will clean hard to remove soiling and help prevent future problems (see more below). Our GP or a Trauma Kit fixes scratches and scuffs.
For scratches do the following:
Try to find the problem scratch by where on the CD you are getting skips or distortion. The CD will play from the inside out. This means that if you have a skip toward the end, most likely the problem is on the outer edge. However ... if a CD will not play at all it could be a scratch near the center hole of the disc. Also a scratch running from the center to the outer edge can keep the player from pre-reading as it loads data. Close examining should tell where your problem lies or you can just do a general surface application with GP. Note: If you have a real sensitive player soiling like a fingerprint may be the problem instead of a scratch.
Only use repair products on the side without printing. Trying to polish the label side will permanently damage a CD because the side that has printing also includes a mirror like surface that is needed to to work with the player laser and cannot be repaired.
We recommend to always try GP first because alone it takes care of 70-80% of repairs. 
Shake the bottle well. With a soft cotton cloth, cotton ball or swab apply just enough to cover the surface. As our bottle directions state, you want to rub firmly. How long depends on the type of damage. Your goal is to "reduce" the depth or sharp edges of scratches.... you do not need to remove them completely. After you have rubbed, let the CD sit for about 5 minutes and then clean, preferably with CD Doctor Protect (which is also a cleaner). It's easier to remove residue when it's wet or slightly dull and it's best not to let it dry completely. When you play the CD and it still skips you should keep trying by repeating the application and rubbing process, but also trying to pin down the actual problem scratch and concentrating effort to it. Often you will notice sections of the former skip are OK but there is still a little skipping. This tells you you're making progress. Be sure to clean off any residue before you try playing the CD. 
If you've tried the GP 2-4 times and there is no noticeable change it's time to use ultra fine sanding paper "gently" on small and specific areas of damage. The grit you need to use is the 3000 to2000 which can be found at hardware stores or body shop supply stores. In these more harsh treatments you want to do your best to locate the specific area of damage and not do a full surface process... (You do not want to use Acute or sanding on the entire surface). Depending on the shape of the scratch you can rub it in either a circular or back and forth motion. 
There are some fix it websites that tell you that Brasso or car polishes will work. They will to a point BUT have oil based additives that can damage CDs over time, especially recordable media.

After the application of Acute or sanding apply GP as directed perviously.
GP reduces scratching but also applies a polymer coating ... see our product comparison page for more.
In most cases, you are only trying to reduce the depth to a point that GP's coating ability will work. This may take some trial, but is successful 95% of the time and it shouldn't take too long to complete the job. The minutes involved save you money when the price of a new CD is compared .... if you can even find a replacement. 
Make sure to save your application cloth. The abrasives in the GP or Acute will last for many applications and all you need to do is lightly dampen the old cloth.

Special notes: Sometimes you may think a big scratch is the problem and it's not. It does happen that a hairline causes more skipping. This could be because it is more abrasive on the edges and is causing deflection while the large scratch is more like a scuff with rounded edges.

Older CDR, CDRW and DVDR/RW may not play because the information layer has degenerated. Factory recorded CDs are "pressed" and will last indefinitely BUT R or RW media has a dye layer that is recorded to. Dyes fade from light alone and this fading also damages the data. Supposedly this is much less of a problem with newer or higher grade recordable media.

Save money!
We've mentioned cost before and this is a good point to talk about it. There are 3 factors we all need to look at when we determine if something is of value. How does the cost of a product that repairs something compare to the cost of replacement? What is the life span of what is being bought and does it outweigh the cost? How much is given for the money?
The simple answers can be seen quickly. A music CD averages around $15.00 and ROM's can run hundreds of dollars. A DVD is in the $15-$30.00 range. 
Each of the CD Doctor products has the ability to provide up to 100 applications per bottle. A repair of scratches with GP or a combination of Acute runs about 10 cents and takes a few minutes to complete, depending on the severity of damage. The treatment will last a long time and it's quite possible the average person may only purchase one bottle in their life....unless you are buying a "lot" of already scratched CD's.
Protect (cleans and protects from damage) costs about 6 cents per application and lasts. If a CD is used seldom, it may never need to be treated again. Used often, it may be months between applications. Protect is so affordable it could be applied to every CD in your collection.

Special note on Protect ... Protect adds a micro layer of "slickness" that repels soiling but also gives a degree of UV protection. This is an added benefit for R and RW media that has a dye layer that is susceptible to light.