If above solution doesn't fix your problem, this may be worth a try:
Steam
Checking File Intergrity
Launch Steam > Go into Library > Find Black Ops Singleplayer/Multiplayer/Zombies > Right Click on Black Ops 2 Singleplayer > Properties > Go into "Local Files" Tab > Click "Verify Integrity of Game Cache" > Wait for Process to finish > Repeat for Multiplayer & Zombies. Launch the game again and see if your problem is fixed.
This checks all the files that the game requires, and makes sure that they are all there. I had a problem and my Black Ops II did not install correctly, I followed those instructions and Steam downloaded the needed files and my game worked correctly. Good Luck!