Randomly being brought from the game into my desktop

Hey guys.

I haven't played League in awhile, and this is only happening now: sometimes, in the middle of a game, I would suddenly be taken to my desktop. Not a windows update or an anti-virus program wanting to update, just randomly being at my desktop in the middle of a match. Of course, I only need to go back into League and the matter is resolved, but that usually takes the computer a few seconds to "recover" from. Needless to say, if this happens in a teamfight (or any fight), it could lose a match. I play League on fullscreen mode, in case that's relevant.

I have found no means to replicate the bug, as there doesn't seem to be any rhyme or reason. It can happen when I walk/farm/fight, and it can be twice in a match or once in 5 matches.

Any ideas what could be causing this?