Check that the external device is connected to the tv with an hdmi cable and is powered and switched on.
Lg tv not connecting to cable box.
Some users have had success using the lg bluetooth rolly keyboard but this is not officially supported.
Press the smart button on the remote control and select settings option set the universal control on the tv menu press wheel or enter to continue.
Make sure the other end is secure in the cable box.
Simply connect your usb cable s to any available usb ports on the tv.
Bluetooth mice and keyboards are not supported.
Once the box has rebooted turn the tv on and use the lg remote s input button to select hdmi 1.
Plug the device back in and power the device back on.
Shut the tv off and securely connect the cable box hdmi cable to hdmi 1 on the tv.
Perform the following steps if the no signal message remains.
Now please try this.
Disconnect the hdmi cable from the tv and move it to an alternate port.
If your remote does not have an input source button press the home button then look in the upper right corner of the tv for the input icon and click it.
Change the tv to the new hdmi input to see if the issue.