computer shuts down when attacking drake

this is a very freakish bug...or?

while playing in S.Rift and i go for the first dragon of the game my computer shuts off after moreless 4-5 seconds i start attacking it, this situation happends to me more and more offen, and its a seriouse problem...normally later in game this dont happend that much. i cant get you a screen shot for obviouse reasons.. even if im sure is going to happend i never know the exact moment.

thank you