Guild Wars 2

I upgrade my pc 13 days ago and i playd gw2 normal wit out anny bugs or annything and then yesterday it restarts and i think i click on restart buton by acitdent but after half day it agein restarted and then my pc started to restart iven if im not playing gw2 , my pc isnt owerhiting (when im in game max 47C) can i somehow fix thos restarts or i need to give up on gw2?

edit : i forgot to say when it restarts it dont show error or blu screen it just restart like it lost power , and if i got restart it hapen in frst 5 min of game but some time it dont restart and i play normali

First disable automatic reboot :
http://pcsupport.about.com/od/windows7/ht/automatic-restart-windows-7.htm

If you still get no bluescreens after that its mostly your power supply.