My father has a late 2010 MacBook Air running Mac OS 10.6.7. I don't think he has ever updated the OS, and as a result, he is having problems with older apps not being able to be updated either, so I'm trying to help him update his computer. I tried to download Sierra today (which should run on his computer, according to Apple) but I can't get it to download. The App store opens fine, I can get to the Sierra page, but when I click on the "Get" button, nothing happens. I have restarted the App store and restarted the computer. I can sign into his App store account but when I try to download any apps, I run into the same problem. I'm not sure if he has a current credit card in his account, so I have tried my account too, and when I go to the "purchased" page and try to download anything, all the "download" and "install" buttons are gray and don't work. Help!