The toothpaste trick might be useful too (no joke).
If your disk is full of scratches, these might be filled with dust. You could
Try to put a small amount of toothpaste on your disk and clean it off with some soft material. Move from the centre of the disk and out, not in circles.
Rinse it with some lukewarm water afterwards.
Use the above trick on your own risk. All I can say is that it never did any damage on my CD's