If you have a scratched disc/CD, I recommend Brasso. Now then, this is a METAL POLISHING liquid. It's an abrasive - a very mild, fine abrasive. And if you use this method, you're gonna scratch the hell out of your CD/DVD, but the disc WILL WORK when you're done. This is a technique I picked up from a DVD restoration board:
1. Take a lint-free cloth and pour a small dab of Brasso on the cloth.
2. Using a finger, wipe the Brasso in a straight line from the inner hole to the outer edge, working your way around until the CD is coated. Continue around again so you've done it twice. (There is no need to add any more Brasso. One good dollop at the start will be enough.)
3. Let it dry to a fine haze.
4. With a clean corner of the cloth, start wiping the Brasso off from the inside out, just as you applied it. Make sure to remove it all.
5. Once the Brasso is removed, spray some Windex or other cleaner on the CD and gently shine it up.
6. If there is a deep scratch or mar, use a bit of elbow grease on it to "buff" it out with the Brasso. But always work from the inside out. Do not work in little circles or anything like that.
I have used this technique to bring many many games, DVDs, music CDs, etc. back from the dead. I have only had this trick not work twice (but both were horribly damaged to begin with). Now then, as stated, you're deliberately scratching a CD to hell (even though the scratches are very, very fine - the CD will appear hazy when done as if it's been resurfaced) but this will work 95% of the time. But I would NOT recommend this for a game disc that's valuable or irreplacable. For that, have it resurfaced or professionally buffed out.