Needed a new mainboard. Later the owner admitted to tinkering in the service menu so there's that.

Another result from a google on this finds two other ideas.
1. Unplug all connections. Remove power and wait 10 minutes. Only apply power and try again.
2. Another post found the "button board" has failed. That's the buttons on the side of the TV. They unplugged the connection to that and have to use the remote from now on.

You won't get it repaired out of warranty as this model refurb here is 215 at Walmart.
https://www.walmart.com/ip/Refurbished-Hisense-40-Class-FHD-1080P-Smart-LED-TV-40H5B/47904715

The min shop charge here is 150USD and that's without any parts or repair!