Rust crashing my computer help?

Hi,when i am playing rust for about 20 minutes my computer automatically restarts.This only happens in rust,when i am playing other games or just browsing the itnernet it doesnt happen.Can someone help me plz?.My computer specifications:
ASUS M5A78L-MLX/BR
AMD ATI RADEON HD 6850
PHENOM X6 3.3 GHz

Turn on vsync, and monitor your GPU and CPU temperatures. It’s probably overheating.

Hey how I turn on vsync
and dude to prevent overheatting what can i do? Buy some sort of portable fan pointing to it?

depends if its the GPU or CPU, you can up the fan speeds for your GPU and they cheap CPU cooling fans

[editline]17th December 2013[/editline]

you turn it on through your video card options