It is necessary to have Steam running in order to play any game that has been downloaded. However, users have complained that they keep getting the “Failed to start game (app already running)” error while using CS:GO.
To avoid encountering this error again, our resident gamers listed all the methods in this guide:
How to Fix the Steam "App Already Running" Error
Fix #1: Close the Game Using Task Manager
This method will force your game to close if it has crashed silently or is “hanging.”
Fix #2: Opt-Out of the Current Steam Beta
Fix #3: Verify Integrity of the Game Files
If you get the “App Already Running” error after installing a new game on Steam, it’s likely that the game’s installation files were damaged or lost.
To fix this problem, you can use Steam’s built-in tool to check the integrity of a game’s files.
With these steps above, you should be able to get CS:GO running normally again.