Some problems with Call of Duty United Offensive

My friend had this problem with Call of Duty united offensive. Apparently, he tryed to go into a game, and it said mss32.dll file is missing, so i told em reinstall. he did, and no change. I told em to dump all files relating to Call of Duty and Call of Duty united offensive and then reinstall again. He did, no change. Now when he trys to uninstall, he gets to the splash screen, he gets to demoshield, he hears the CD rev up, and then it stops, and nothing happens. Im not sure what happens, but i am a United Offensive player and this isnt common. mss32.dll files are in any game, but this one is bugging me. How would he be able to regain this file? Any advice and help is appreciated. Thanks.