Lenovo A399 comes with MT6582 cpu from Mediatek. Here you can download Lenovo A399 usb , adb , preloader and vcom drivers. USB drivers are required to connect phone with pc and adb drivers are needed to perform fastboot commands however mtk preloader drivers are needed to flash update phone via mtk flash tools.
Download Lenovo A399 USB ADB Preloader Vcom Drivers
Supported OS : Windows XP / Windows Vista / Windows 7 / Windows 8 / Windows 8.1 / Windows 10 32 and 64 bit