Windows 8.1 update doesn't appear in the store

I lost a lot of time trying to understand why on some windows 8 installation the 8.1 updtate didn't appear. There are multiple reasons why this could happen. But I find I nice and automatic way to detect what the issue is, there a tool from microsoft called "Windows 8.1 Update troubleshooter" that analyze the pc and tell you why it is not appearing. Here the link : http://go.microsoft.com/fwlink/?LinkId=395014 Download it and run it, then follow the instructions, at the end it should say you WHY you don't see the update. Digger