Hanging up on startup

I got a new computer today, and after installing Steam, I downloaded TF2, which works wonderfully. I also installed HL2 for good measure. When I attempt to open Garry’s Mod however, it starts up regularly, the regular background appears, the word “Loading…” appears in the bottom corner, and it hangs up, remaining like that for as long as I have it open, never closing, never any error message or anything. What is causing this?

I have the same problem.

Are you owning a legal version of Garry’s Mod? If you’re not, then that’s your problem. Please include your Steam Profile in the next reply.

Sorry, I forgot the post and the problem is back :frowning:
Here my steam profile : http://steamcommunity.com/id/JaimeLesTrains/