My garrys mod will crash at start up, nothing works that has been mentioned prior to this post

[DRexStone]

Every time I start up game it will open application and say loading then it will say "hl2.exe has stopped working" and I've tried everything mentioned to fix it. I really need help and don't know what to do, I moderate on a server so I really need a fix. This has just started happening today 1/16/16 at 12:00 pm Eastern standard time and no updates or changes to gmod have occurred prior to this. So if someone can help me I would greatly appreciate it.