Get some rubbing alcahol and a soft cloth. Dip the tip of the cloth in the alcahol and rub it onto the cd in an up and down motion. Cover the entire CD with it and when you are done dry it off. That method works for me 9 times out of ten. I have found it to be incredibly effective. If it doesn't work the problem is either A) The game is damaged beyond repair or B) Your PS2 is broke.