Is USB debugging switched on Enable USB Debugging and OEM Unlock, this should allow you to start the “First step” of the Backup support topic
Slide your finger from top of the screen downwards, and click on “Android System. Charging this device via USB” 2 times.You will see USB preferences menu. Select File transfer. If you don’t see this option, try using another cable or another USB port on your computer.
The “device controlled by” is explored in the following thread, where I add screenshots in Post #7. This may help indicate if you are using an unsuitable cable.