Personally, I'd check the connection of the screen to the motherboard inside (if you feel up to it). Search here for "screen problem".

Or, I'd get in touch with Roland.

Regards
Andy

I've no idea about costs and stuff, I'm afraid.

Roland in your country will be best able to advise you on what might be the problem & what the possible solutions are. It sounds to me like you might need a new screen, but I couldn't say for sure.

Your local Roland will also be able to advise you about authorised repairers in your area, if there are any.

Good luck and let us know how you get on!
Andy