If a full factory reset doesn't correct this then I suspect you are looking at a hardware issue, which isn't good.
⦁ To force a factory reset, please use the following procedure:[br]
1. Unplug the TV's power cable from the electrical socket.[br]
2. Press and hold down both the centre and down buttons located on the TV.[br]
3. Plug the TV's power cable back in the electrical socket (while still holding both the centre and down buttons).[br]
Please note that this force factory reset is to be considered as a last resort, as this will remove all the settings, self-installed applications, channel sorting etc.