GMod closes instantly while playing

ok so my pc can run gmod and everything, my pc can run arma 2, crysis ect

anyway this has happened for sometime, but im playing on any server like zombie survival for example, it usually happens there, and while im playing the game just closes without any warning ive turned all graphics to high and disabled 16x anti alising? but still it does it

how do i fix it?

Install the zombie survival yourself so it can read it from server or whatever.

Does it come up with an engine or memory error?

nope just an instant crash