Recently changed my HD and reinstalled the original OS X Leopard, trying to get my previous purchased OS X Mountain Lion was a problem, contacted support the solutions provided that are links to Apple from a guy located somewhere in India where no help, even providing all the facts of the problem as OS installed, inability to see what he saw from his side, my installed OS system is not the same he is advising me from, his best solution was to call apple support, he never got a little further of seeing this fact, it was my own search for answers that found the solution.
After a long troubleshooting and research in order to get access to now days features from the store and Itunes need to have installed OSX 10.6 or better, any update would be to the standard of the OS X installed and your computer and it will be up to date according to the installed version.
Bought a 10.6 OS and from there everything started to appear in the store and itunes, found my purchase it was hidden a feature available at the time when installed the Mountain Lion and hid it. You can not access this feature if you have itunes installed with the Leopard version.
So botton line, Leopard or below you will not be able to access all the features from now days in apple, if you have a purchase as a OS X, before you change or format the HD make sure you have OS X 10.6 or better if your Mac is +3 years old.