Gmod wont launch

[Sedative]

Help! I am new to gmod only buying it after watching videos from this server and after buying and downloading i click play and it acts like its about to load for a second but never does or will run in the background according to task manager.

 

[Leon]

Go to your steam library -> Garry's Mod -> Right click, go to properties -> Local files -> Verify integrity of game files and let me know if it works. If not, I will look into it further for you