Sounds like your box is in single cable mode.

Did you set up the box with one cable and add a second cable later ? If so carry out a factory reset and watch for the two cables found message.

Goto Menu/System/Diagnostics and check you have signal and quality for both tuners. If not look round the back are the two cables on the outer sockets with nothing on the middle one ? If not power off correct the connection and do the factory reset. If they are on the correct sockets check the tuner 2 f connector. Male sure that a whisker of screen is not shorting out the connection.

If you are operating the box with only 1 cable the short coax loop from tuner 1 out to tuner 2 in must be fitted.

You can check what mode the box is in by using the secret menu.

Open the Setup menu

Press Red Green Yellow Blue Green Yellow Blue

Connection type should be Two Cables (Same)