I also had this problem.
If I follow the information given by Microsoft, I'd already thrown away my device...
To be able to upgrade to Windows 8.1, you should have applied all Microsoft Updates.
So I checked and it downloads updates and installs it.
After a reboot you should have the Windows 8.1 upgrade in the store.
Which I hadn't.
Then they state that you need KB2871389. I downloaded this patch and installed it.
Again a reboot is needed and while rebooting it stays on "please do not turn off your computer, applying updates" (or something like that) for 30 minutes on 15%! After 45 minutes he has finally restarted.
Then I see that the Microsoft 8.1 upgrade is available in the store, but I cannot even download it because according to Microsoft I need an account with administrative privileges.
Which I have!
I checked my account even twice to be sure I'm not dreaming, I even create a new account with administrative privileges and I enable the build-in administrator account.
Nothing works...
Microsoft! Why are you doing this???
Now I found out about this wsreset.exe, I execute it, restart the pc, but no Windows 8.1 upgrade in the store!
No I checked if there are no Microsoft updates available, but I'm up to date.
I also had the KB2871389.
So I decided to uninstall KB2871389, restart the computer and install it again. Reboot took again 45 minutes!
Then finally I have the Microsoft 8.1 update in the store and I could download and install it.
Microsoft is complicating life... and it's by my knowledge the only company who sells stuff that never works for 100% and they earn tons of money with it and after all these years they still get away with it...