It's a sign the unit can't 'see' the operating system.
Try a pin reset if your model has that. Or, connect to the computer, use Explorer to remove all the loose files in the root of the unit but NO folders or their contents. Then start up TTHome. Select Update. It should detect that the operating system is missing and offer a download. Accept and let it install it. Now try and see if the unit works.
Before removing the loose files, use Explorer to make a complete backup of the unit's contents first.
Another way is via TTHome. Move to the screen for Remove items from my unit and select 'application'. You'll get a warning but that's the one you want. Make a Windows Explorer backup first, though.
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