1.Go to /c/Programms(x68)/Steam/SteamApps/common/And Copy'n'Paste the Call of Duty Black ops 2 File anywhere you want (Steam needs to be Off)
2.Then Start Steam again,Uninstall Zombie,MP,Singleplayer.
3.Install Everything Again.
4.Verify Game Cache Like Birdpoop Said.
5.And Everytime it wants to Download Again Just Delete The File that he want to download again and but the copy'n'paste thing there. but u have to use the copy'n'paste file right after it want to Download. Hope i Helped