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.
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.
Disconnect the cable box from power for 10 seconds to reboot it then plug it back in.
Change the tv to the new hdmi input to see if the issue.
Shut the tv off and securely connect the cable box hdmi cable to hdmi 1 on the tv.
Some users have had success using the lg bluetooth rolly keyboard but this is not officially supported.
If your remote has an input source button press it and choose the input from the list that matches where your device is connected.
Make sure the other end is secure in the cable box.
Bluetooth mice and keyboards are not 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.
Perform the following steps if the no signal message remains.
Simply connect your usb cable s to any available usb ports on the tv.
Unplug the power to the external device for 30 seconds.