I have been trying to play gmod lately but it just seems to just shut down on me with out any errors but if i look in the folder i get this thing. The crash is hl2_140711_crash_2014_7_12T14_29_29C0.mdmp
First thing I can suggest is that you verify the integrity of the game cache. This can be done by:
Right clicking Garry’s mod in your steam library > Properties > Local Files tab > Verify Integrity of Game Cache.