There seems to be a somewhat random problem with the elevators out of Blackreach. Activating the elevator's lever will exit Blackreach and then enter into an endless loop of entering Skyrim (or in the reverse direction) which overwrites all of the current autosaves and forces the use of task manager to kill Skyrim.

Apparently, I am not the only one this has happened to: http://www.uesp.net/wiki/Skyrim_talk:Great_Lift_at_Raldbthar