Microsoft's Windows 8.1 RT upgrade is temporarily unavailable as the software giant is rushing to fix an issue that can cause boot problems on some Surface tablets. On its website, Microsoft explains they're working to resolve the situation asap.
Windows RT 8.1. Microsoft is investigating a situation affecting a limited number of users updating their Windows RT devices to Windows RT 8.1. As a result, we have temporarily removed the Windows RT 8.1 update from the Windows Store. We are working to resolve the situation as quickly as possible and apologize for any inconvenience. We will provide updates as they become available.