Need help. Touchscreen not working LG G3
To answer the part about using the phone even though the touchscreen doesn't work:

You can use an OTG cable, to plug a computer mouse into your phone and you will then be able to navigate through your phone with it. This way, you'll be able to allow your phone to connect to your computer.

Here's an OTG cable that will allow you to connect your phone to the computer while having the mouse connected.