The "Steam must be running" error in DmC: Devil May Cry often results from a failure to detect the Steam client, solvable by deleting the ClientRegistry.blob
You may find forum threads suggesting you create a text file named steam_appid.txt inside the game folder containing the game's ID number. While this can work for pirated versions, it often causes issues for legitimate owners because it can bypass the standard launch parameters Steam expects. The "Steam must be running" error in DmC:
Close Steam completely (check Task Manager to ensure it's not in the tray). Navigate to your main Steam installation folder (usually C:\Program Files (x86)\Steam Find the file named ClientRegistry.blob and delete it. The "Steam must be running" error in DmC: