Are you getting a (like 0xc000007b) alongside the DLL message, or does the game just fail to open?
If you are running a version of the game that isn't syncing with Steam properly, you might be tempted to download the DLL from a third-party site. alien vs predator 3 steam apidll work
For 90% of players, through the Steam UI will solve the problem instantly. If the error persists, it is almost certainly your Antivirus blocking the file from loading. Are you getting a (like 0xc000007b) alongside the