Cause 2 of 2: Tethering isn't used correctly
To use tethering, your phone and your computer need to be connected and set up correctly.
Solution: See how to use tethering.
1 Connect phone and computer
Connect the data cable to the socket and to your computer's USB port.
2 Find "Tethering & portable hotspot"
Slide two fingers downwards starting from the top the screen.
Press the settings icon.
Press More.
Press Tethering & portable hotspot.
3 Turn on tethering
Press the indicator next to "USB tethering" to turn on the function. An internet connection from your computer via your phone is automatically established.
4 Return to the home screen
Press the Home key to return to the home screen.