Cod4 and world at war

Hello,
i bought both games and had no problem with cod4 until a month ago. i kept having problems with the game booting me out. so i uninstalled the game. now i put the disc in and it doesnt even recognize i have a disc in the drive. i put world at war in and the same thing is happening it wont recognize the disc is even there. ive tried loading other games and cds in the drives and everything works except cod....