UE50JU6800 tv has sound but no picture

[Nicb]

Hi I have UE50JU6800 tv which has sound but no picture , no menus appear when select from remote  , you can change channels via the remote and hear the appropriate channel.  Any ideas ? 

[AndrewL]

@Nicb: Do you have any external devices connected to the TV such as a set top box? If so, try connecting to an alternate HDMI port to see if this helps, or try another HDMI cable. If you power off the the TV, unplug it at the wall for around 30 seconds, then plug it back in, does the issue persist? 

[Nicb]

Have tried different hdmi cables /ports and have powered off for several minutes - no joy