Almost instant crash!

I was booting up gmod for a machinima and after the menu loaded it crashed!
I have no idea what happened, please help!

Please list all the workshop addons that you’ve subscribed to.
Also, verify integrity of your game cache.
You can verify it by going to your steam library, right clicking the game, going to properties, and go to local files. Then, there should be an option to ‘Verify Integrity of Game Cache’.