Hello and sorry you're having problems.
If there's no signal on the screen then it's caused by either of the things below:
1) TV's not set to the correct Input (use the Input button on the LG remote to switch).
2) The HDMI cable is intermittent/not working on this TV (HDMI is digital and a cable can indeed stop working on one device yet still work with another). I would suggest trying another HDMI cable on this set.
3) The Mainboard on the LG TV has lost it's HDMI ports- which is a common failure in these sets. This does require replacing the Mainboard of the TV which is a plug and play component. However it would be worth trying a hard reset of the TV.
Unplug the set from power, then remove any HDMI cables from the TV.
Press and hold the power button on the TV itself (not the remote) for 10 seconds and release, then wait a minute and reconnect the HDMI cable to the set. Plug the TV back in and power it up. Select the HDMI Input that you'vve plugged into (HDMI 1-4 respectively).
If you're unable to find the solution based on what is posted above, then I will need to know the full model number off of the back of the TV as well as how long you've owned it for.
Feel free to reply back if you need more help, or want to reply back with more details. It does not cost you anything more to reply back once you've rated. Please do rate me positively (at least 3 STARS) and I will continue with you until this is sorted. The positive rating ensures I am credited for my work.