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Sometimes if the itunes store / apple store server is down, it will force the device onto the home sharing screen.
To isolate whether that is whats happening, try using your computer, opening itunes, and then going to the store page. If you can get there, then we know the issue is with the Apple TV itself.
IN t hat case, try disconnect all cables from the apple TV for 30 seconds. Also, unplug your modem and wifi router from power for 30 seconds. Then plug all back in.
If you still get stuck on the home sharing screen. Then follow the steps below to use itunes and restore the apple TV.. This will definitely fix the issue.
If you have further questions or run into any issues, let me know.
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Senior Technician and Network Switching Systems Operator / Maintainer.