Somtimes when i'm in a duel or fighting someone in BGs if a lot of spells go off at the same time the game freezes for a second and then completely crashes, instantly bringing me back to the desktop without a single error. It usually happens when I press a lot of buttons at a same time for example when I pop cds etc...
Hey Borab, it may be easiest for us to figure this out if you attach your diagnostics and a trace route to a ticket for us to review. After that's been sent in, you can PM me the ticket ID# and I'll be happy to get back to you as soon as I'm able!