If you're using Windows 8 Pro just like me, the Windows Store is disabled by default.
If you installed Windows 8 normally through a disc,or installed over internet or bought a new machine installed on it,Windows Store comes active by default.
If you installed it to a USB disk,then it installs it as a Windows To Go workspace which proves deactivation of Windows Store that comes by default.
See here for more information: http://technet.microsoft.com/library/hh831833.aspx#BKMK_wtgdif
Whenever you run a Store Application from a newly-named Modern (Metro) UI, it says:
Here is the solution:
1. Run gpedit.msc
To run it, use the key combination Windows + R
2. Get to Computer Configuration->Administrative Templates->Windows Components->Store
3. Edit "Allow Store to install apps on Windows To Go workspaces" and set its value to "Enabled" and then click Apply
That's enough for running Windows Store and installing apps but if you need further editing you can also:
4. Edit "Turn off Automatic Download of Updates" and set its value to "Not Configured" or "Disabled"
This will install any update from the Windows Store.
So generally,when you run a Store application, you'll now see it fully activated!
Now you can use it gladly :)