Download Lenovo A3900 USB Drivers Latest Version
Lenovo USB Drivers Is very important and required files that manage you connecting your Lenovo A3900 to PC.
So when you installing those drivers on your PC you can connect your Lenovo A3900 to transfer data (normal connecting), and also connect your Lenovo device to Flash and upgrade Stock ROM (Firmware).
Quick Lenovo USB Driver Installation Guide.
Step 1: Extract The Drivers File.
Step 2: Run Setup File.
Step 3: Click next and select your language.
Step 4: Wait one minute.
Step 5: Click Finish Button.
Step 6: Now connect your Lenovo Device.
See full tutorial : How to install Lenovo USB Drivers