Television won't come out of demo mode

We have a Sharp LC32CHG69021K TV. For the past week whenever it is switched on, we have to go through a first time installation in order for it to work. On switch off it goes back to having Poland as its default. Then there is the model number emblazoned across the top left hand corner of the screen and a big K underneath in a blue box. This remains on the screen throughout. The only time this disappeared was when my 5 year old sat on the remote control. I have tried all the remote control buttons and they do not get rid of this notice on the screen, nor did sitting randomly on the remote control myself!

We were having another TV repaired and the repairer said that he thinks that the TV is in demo mode. If this is the case, how do I switch this off and get this to remain in normal set up?

Would really appreciate any help and advice please.