Connect your Android phone to PC via USB cable, turn to the home screen of your device, drag down the list until you see the "MTP mode". Just select it!
1. For Android 4.0 or above, you can go to "Settings" > "About Phone" > "Build Number". Tap it 7 times until "You are now a developer" turns up. Then, back to the previous screen and hit the "Developer Options". Now, check the box next to "USB debugging" to enable it. For other Android versions, please refer to the guide.
Connect your Android phone to another port in PC to rebuild the connection. You can also connect via the original USB cable which has been factory tested, to replace a 3rd-party sourced cable.
If you find that the USB driver can not be installed automatically after your connected your Android device to the PC, you should download and install the proper OEM (Original Equipment Manufacturer) USB driver manually according to the brand of your phone. And if you have any anti-virus software installed in your PC, you will be popped up with a note where you should click "Allow" to get the USB driver downloaded and installed.
Download AirDroid on both your Android phone and PC. Launch it and sign in the same account in the mobile and desktop AirDroid. After that, you can get the Android phone connected with PC via WiFi.