hl2.exe Has stopped working. BUT Gmod still plays!

Whenever I play, at random I will get the fated “hl2.exe has stopped working screen,” but at one point I noticed I was still falling. I then drag the error to the side (beings I can’t close it without closing the game,) and just continue playing. This isn’t really a problem for me, but it’s just rather weird. No other game has done that before. Another thing is that when I overclock my motherboard, it will “hl2.exe has stopped working,” BUT it will actually crash! It might be that my something on my motherboard will “skip,” but I’m no computer geek.

Thanks.