gmod crash on start up widnows

when i tried to open gmod 3 hours i had just been playing it after the computor was turned off and a the logo never apeared and it said hl2.exe (garry’s mod) has stopped working. a problem caused the program to stop working correctly. anyone know how to fix this and i already restarted my windows 7 computor. PLEASE HELP ME! also my friends are able to run it without it crashing.

Validate TF2 and CS:S.

what does tf2 and cs:s have to do with it? and how

Just do it. Trust me.

how though and also i dont play CS:S i dont think i have it instaled but its in my shared lib and how do you validate something?

[editline]22nd March 2015[/editline]

and my friend just started gmod and said its working fine

Do it for TF2 and CS:S if you have them installed obviously.