"after update" steam games crash without error warning.

[maskedmoose]

two days ago i ran up steam to play gmod. i installed it and updated it and once i pressed "play gmod" the game opened a new window but then in 3 seconds closed, without an error. i already tryed to reinstall steam and garrysmod but nothing works, not only does garrysmod do this but all of my games. please help i jst want to play garrys mod. :(
- moose