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.