Firstly, check to see that the USB cable is correctly connected. Try to use another cable and make sure the USB port on your computer is working correctly.
In some devices, you can check the USB connection type. For your device running Android™, you could have:
- MTP: it can be the default connection type. It requires Windows® Media Player (11 or later) for a computer running Windows or Android File Transfer for a computer running MacOS
- PTP: files can be copied only in the "DCIM" and "Pictures" directories of your device. A driver is installed at the first connection
- Mass storage (MSC): you device is identified as an external storage and you need to approve the connection. A driver is installed at the first connection
- Android Debug Bridge (ADB) : connection mode that is for app developers
To check your device's connection mode, go to Settings 
(or
) Storage > 
then go to Menu 
(or press the physical Menu button of your device) to display USB computer connection.
One of the frequent causes for a device not bing connected is that it is in ADB mode. Deactivate from Settings > Developer options 
. Make sure USB Debugging is unchecked.
If your device is set up for MSC (mass storage), whenever you connect it to a computer, you will need to confim by pressing OK in the pop-up window.
