'''++@andyspeariett++''' … this is indicative of corrupted software or faulted eeprom. This could also be a bad mainboard in general, but i would start with the software. visit the manufacturers site and download the lastet version of the firmware.
https://www.samsung.com/uk/support/model/UE40D5520RKXXU/
follow the instructions completely and entirely. if the set takes the firmware and continues to show the same symptoms, further troubleshooting is required.
if the set doesnt take the firmware, it could be a bad eeprom that isnt able to be overwritten with any code. you may be successful in replacing this eeprom and flashing the latest firmware after.
if this fails, can troubleshoot further to narrow down the problem. Will require a multimeter and ability to use it.
try the aforementioned solutions first, report back with success or what you have done and we can continue if need be.