If you upgraded to Windows 8.1 on a Surface RT last week, there was a chance your tablet got bricked. Microsoft now has a solution to hand -- but it's not a small download.
The Surface RT recovery image weighs in at 3.7GB, which means you'll need a decent sized USB drive to install it to. It should return a bricked Surface RT to factory default -- a timely reminder that backup of your own files should be a first step, not a last minute emergency step -- and get you back up and working.
Surface RT Recovery Image [Microsoft]