Pro is installed, the question is, is it the Volume license edition? If it is, that may be why it won't upgrade to 8.1 through the Windows Store. One way around all this is to go back to the original version installed at the factory. You can download Windows 8.1 Single language install media here,
Create installation media for Windows 8.1 - Windows Help . That install media will read and use your Embedded OEM key that is in your BIOS, even Windows 8.0 keys. This will get you back to a legally activated OS and no having to upgrade from 8.0 to 8.1, you just go right to 8.1.
option 5 here,
http://www.eightforums.com/tutorials/27129-product-key-find-windows-8-a.html, should list your OEM key and the pro key currently in use, if you want to record it before doing anything. You don't need to know what the OEM key is, just that it does exist. If you think you might want to try installing Pro, write that key down too.
If you click the blue "view details of windows activation on the system screen it may give you more info to help you sort out what's installed.
http://www.eightforums.com/tutorials/18309-windows-8-windows-8-1-iso-download-create.html
http://www.eightforums.com/tutorials/15458-uefi-bootable-usb-flash-drive-create-windows.html
http://www.eightforums.com/tutorial...e-firmware-interface-install-windows-8-a.html