It is advised to uninstall those programs or disable their Overlay functionality and try to launch the game again if you are having start up problems, such as black screen on start up. There are a few programs that may interfere with Garry's Mod and other Source Engine games, such as: Uninstall or exit programs that are known to cause problems If you have Team Fortress 2 installed, you should complete steps above for it, and any other installed Source Engine game as well. Lately Team Fortress 2 started to cause problems with Garry's Mod. You can learn more about game cache verification here Verify Team Fortress 2 and other mounted games, if any
Press 'Verify Integrity Of Game Cache' button.Select 'Properties' from the dropdown menu.If that doesn't work for some reason, you can do it manually: Sometimes game files might get corrupted and a file verification is necessary. If when you start Garry's Mod the screen is black - your display settings might be wrong.
