I have a late 2009 / early 2010 model iMac with core i5 CPU. I'm trying to upgrade from OSX 10.6.8 (Snow Leopard) to 10.10 (Yosemite). When I try upgrading in the App Store, nothing happens. I restarted my computer, have no apps running, and select "GET" for Yosemite in the App Store application, and nothing happens. The button is I selectable after I click it, but nothing happens. I can't select it again without reloading the page, but the download never begins. I get no error message or anything. It's not a browser issue as I tried launching the App Store from Safari and Chrome. I've also checked the Yosemite requirements page and all iMac from 2007 onward can be upgraded. 10.6.8 is the oldest OS which can be upgraded and that's what I'm using. Can someone please help? Thanks.