This has already happened to me on bo3. Sometimes, some Steam games may download files automatically for no reason whatsoever. You should later change a Steam parameter in the Black Ops properties so that you don’t have to do an automatic update.

I don’t know if it can help you, but once for my game BO2, he didn’t want to open up. I reinstalled it, it didn’t work, then I selected an access path for Plutonium Luncher, and this time it worked. So try "maybe" to change the path for your game. Try to select the folder that contains all the game files (e.g., Plutonium T5 Full Game Files). If it still doesn’t work, I can’t help more bro