If you lost your menu on the TV set, I really doubt that it's related to an incorrect setting in the first time setup.
Sounds more like the TV's computer completely locked up or your display panel lost it's drive voltages that light up the screen.
Unplug the TV set for 5 minutes, so the computer can reset itself and reboot. Plug it in and turn it on. If it was just locked up, you will have access to your TV's menu. If it's still missing, you got a TV set that died the moment you turned the TV on the second time.
I've seen that happen. In those situations, I don't even think twice about telling my customers to call the store it was purchased at and talk to the manager of the store, tell them you want to exchange the TV for another one.
To me, that's the right thing to do and the store should be more than happy to exchange a defective new TV for one that works. You shouldn't have to wait to get a brand new TV serviced by a Panasonic authorized service provider and I am one.
So seriously, try the 5 minute unplug and if it doesn't recover, call the manager because they have the ability to make issues like this right with their customers.
They should exchange the TV, just because it's the most convenient thing for you.