You have sound but no picture.

First thing to try, is pressing the MENU, or VOLUME control button on the TV remote control.

If you see any symbols on the screen, this means the screen is actually running, but not displaying a picture, the TV may require adjusting of the settings, or the wrong input has been selected,

If you are watching the program through a Foxtel or set-top box, it could be that either of these devices are not running or have not been selected on the TV.

It is also possible that the TV will not feed the picture through to the screen, this means you can see a menu and change inputs etc but no other picture will appear on the screen, this could be a fault in the processing of the signal on the main board etc.

Any of these situations can be checked and addressed by a technician.