Microsoft pulled the Windows RT 8.1 update from the Store during the weekend after discovering that it bricks some tablets, but the company is still looking into the problem right now.
In the meantime, Redmond has launched a recovery image for Surface RT
tablets that would help consumers get back to Windows 8 and make their devices usable once again. As
WindowsObserver notes, the Windows 8.1 update is still unavailable at this point for RT devices, but at least you can start using the table once again.