Guess if the android sooner driver yet install?
ZTE Handset usb driver installed.
If connected phone to pc under "connect to pc software" usb mode, & had usb debug mode enabled.
a device: zte handset adb handset could be found in device manager
under command window, type:
adb reboot bootloader
phone should reboot & stop at logo /blank screen
"zte handset adb handset" should be gone & changed to "android sooner single adb interface" in device manager
if there's any android phone related drivers not found displayed in device manager, manually update the device and point to the folder: your drive:\program files\zte_handset_usb_driver\drivers\
to install missed drivers.
Then type in cmd :
to verify ...