When attempting to repair a CD, it is best to start with soap and water, or a mild cleaning solution of rubbing alcohol and water. Only after attempting to repair your CD with these solutions should you move on to using more abrasive cleaning solutions, such as toothpaste or Brasso. Although these solutions will allow you to wear away the scratches on the surface of a CD (because of their gritty texture), they will also wear away part of the plastic layer of the CD, which could potentially lead to data loss.
When cleaning a CD you would like to repair, use a soft cloth to scratch the CD as little as possible. As you wipe the CD with this cloth, always wipe across the tracks from the inside of the CD outward. This will avoid scratching the CD along the tracks while cleaning it, which could damage your CD further. When finished cleaning, always allow the CD to dry before testing it.
Always back up the data on your CD once you have repaired it. You never know when the CD could stop working again in the future. This can be done using software that is already installed on your computer to burn a copy of your CD. When using a PC, Windows Media Player can be used to copy your CD. When using a Mac, iTunes can be used to copy your CD.