I deleted that previous response because the User (now blocked) added a spam link.
Did the TV suddenly start behaving like that (in which case it may be a fault), or is there a possibility that someone has gone into the Picture or Service Menu and adjusted the settings?
If you want to look in the Service Menu, the following is from the Service Manual:
The Service Menu must be activated while the TV SETUP menu is displayed. From this initial state, the Service Menu is activated in the following way: Beo4: the Service Menu is activated by pressing 0 0 GO within 3 s.
Be careful to note any settings before adjusting (maybe take a photo). You may also want to try resetting the TV to factory settings, which is one of the options in Service Mode.