I have a LeTV android phone launched in India in 2016, now the company has been shut down. Few days back, my mobile screen suddenly just went off. Now it is just switched ON. Before dismantling it, I want to transfer my data to my PC as I haven't set backup on. I tried through command prompt adb commands but it is saying device in unauthorized, do it by clicking on screen which I can't do. Please help me, how can I transfer data.
ADB commands won't work if you haven't set up USB debugging prevoiusly, and also allowed your computer to debug the phone.
If I understand you correctly that your phone only turns on, but you cannot see anything on the screen, I am afraid nothing can be done. Take your phone to a person who can fit in another display. Otherwise, this seems virtually impossible.