Windows 7 & 8 have conflict issues with the older games that the games were not designed to work on, yet while I have the same issue you have I just keep trying and I eventually get in and play. This is not only on COD4, but COD5 as well. If you keep retrying eventually you will get in and be able to play. One thing that helps is, while you are playing, disable your real-tech sound card in the sound control. It doesn't totally get rid of it but there is something with realtech and the older COD games that they have conflicting issues. I have had this issue ever since I installed Windows 7! Good luck cause I wanna cut your ass!
i had the same issue with xp its not limited to win 7 and 8