Go to Android Developers
Download Android SDK Manager and Android - 5.0 Lollipop for Nexus5/Nexus7 images.
Install Java JRE 8
Install Android SDK
Use the commands under cmd to check your device is exist.
adb.exe devices (Power on)
or
fastboot.exe devices (Fastboot mode)
Unlock your device.
fastboot.exe oem unlock
