I have a 1st generation ipad with 3G, and for the last several months, it will not download new apps or update old ones. It does connect to the internet without a problem. When I go to the app store, it searches for apps, shows them as available for download, and when I press the "free" button, the "install" button shows up, but when I tap it, absolutely nothing happens. It is as if the button has become unclickable. Any thoughts?