My solution to cleaning my Disc's and getting them to work again.
Get your Disc and place it in a Basin or Sink of Hot Soapy Water (Preferrably WASHing up Liquid) and use a Soft cloth and wipe it. Take it out and Dry it with a Soft Towel making sure not to lean hard or Scratchs might happen, then simply put it back in and see if it works.
May think that's crazy but i've been doing it for the last 3 Years with all my Games that are very Dirty or simply to Scratched.