It happens at random (this afternoon’s was when fighting the World Boss) - the game client dies, the screen goes black, and the keyboard and mouse stop responding. This has happened several times however this time it corrupted BattleNet requiring a reinstall.
I am aware that plenty of other people have reported it - it needs urgent attention.
Exacly happend to me tonight. Not once, but twice. At boss. I dont understand how this game even got released with this big of an issue. Totally insane if u ask me.
Can i ask for refund?
Update they will not do a refund 
I had this issue regurlaly and PC lockout helped. But today the first time when I even could not poweroff. The system did not react even to this power off button.