When I encounter people trying to solve HDMI-related problem, I invariably, immediately recommend switching over to component cabling. The picture is better, and there are far less issues with both HDCP and resolution switching issues.
That said, on to the problem you requested help about:
First I recommend you unplug all signal and power cables to your set and walk away for a good ten minutes. This ought to reset the brain inside your TV into thinking it is being setup for the first time. Reconnect the antenna, power and signal cabling, turn your set on, and run through the Auto Search function of your TV's on screen display setup menus, taking care that 'AIR' is selected as your TV's Tuner Mode (it will have most likely reverted back to 'CABLE'). This ought to help it find your antenna's DTV channels.
I hope that helps.
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