Like you already said:
Unauthorized means that your is not trusting your computer. This is because after activating USB-Debugging and connecting your phone to your PC, there should be a popup asking you if you want to trust this PC, which you have to agree (permanently).
The issue now is that you do not get the popup. I also had this issue (on another device) and installing other USB drivers solved the problem. Maybe you try the official standard Android USB driver.
If this does not work too, try other drivers or if possible try it on another PC. Also try to disable and re-enable USB-Debugging (and reconnect USB) after installing new driver.
Before installing new drivers, make sure to remove all of the old broken drivers with USBDeview (Download at the end of page). You need to unzip it and !run the program as administrator. Then it creates a list of all USB drivers installed on your PCs (pay attention, as there are also drivers for other USB devices like printers or USB sticks).
Select all unwanted old Android USB drivers by holding CTRL and selecting one entry after another. If you have selected everything, release CTRL. Then click on the remove-icon or right click on any entry and click remove. Then the installed drivers should be cleared and you can install the new one.