Windows 8.1 no more avaliable

Microsoft has temporarily pulled the plug from its 8.1 online download from its store.

According to Microsoft the problem was

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. 

Windows 8.1 adds a Start Button, boot-to-desktop option, and other updates designed to improve the usability and appeal of Windows 8.

The Windows 8.1 is an addon to the Windows 8 available as a free update