Hi, i got those probleme too. I think (not sur) it appends for me when alt+tab too much, or running deezer or some internet site that autorefresh regularly.

Sometime i play during 5-6 hours with no crash. Sometimes it could happen exactly at the same place, for exemple : In some instance i know that i have a very high chance to crash at a specific mobs pack or place..

I have 3 type of crash :
-PC freeze, and can listen music or sound but nothing respond -> i need to hard reboot
-PC Freeze, but i can acces to task manager ->game will close automatically, no reboot needed.
-PC freeze and game close automatically, no reboot needed.

In the other side, i think my psu is very limited and i should change it, it cause very very rare pc shutdown and rebooting alone..

My driver is 320.18 (nvidia).

My rig is :

i7 extreme 3970X @ 4.5 ghz.
MB : rampage IV extreme.
32 GO ram @ 1866.
SSD Crucial M4 500 go (where the game is installed)
SLi gtx titan.
PSu : seasonic platinium 860W..