I have a scratched call of duty four disc, I can sometimes get to multiplayer games, and cannot play single player or some multiplayer maps. If I download call of duty four onto my hard drive from my friend's disc, can I then play it fully by using my disc to start it up as well as the downloaded call of duty four to play the game?
I can see it working if I understand correctly: You want to use your friends disc to install the game and then use your own game key to play? Best to give it a try and see! Best option would be contact the company, who can send you a replacement disc with little cost.
