Xbox unreadable disc?

so ive been playing this same game for a while now and when i put it into my xbox today, it said it was unreadable. i played it just yesterday and now its not working! other discs are working. i already went through the procedures on the xbox website, but nothing worked. i wiped the disc with a slightly damp soft cloth, but i guess that wasnt enough because im assuming its because the disc is in bad shape. can someone please tell me whats wrong and how to fix it?? thanks