garrys mod starts up then the starting screen turns invisible NEED HELP!!!!!!

when i open garrys mod on steam it opens and it doesnt crash but the start menue is invisible i know the game is open because when i move my mouse i can her the sounds when you go over a word like join game e.g
need help

What OS? Windowed or full screen?

[editline]8th August 2015[/editline]

Can you open console by holding the tilde key?