Troubleshoot guide for updating the adb and fastboot drivers manually in a PC running any version of windows
First, try updating your drivers through windows update automatically. If the drivers are installed and still fastboot commands are not working, then follow these steps:
* PC running windows 7/8/10
* Internet connection (just 20MB)
* Working USB cable
(1) Download the [OFFICIAL][TOOL][WINDOWS] ADB, Fastboot and Drivers - 15 seconds ADB Installer v1.4.3 from XDA
(2) Install it with "Y" confirmation for all 3 options and reboot the PC
(3) Disable the internet connection of your pc
(4) Reboot your phone to fastboot mode and plug it to your PC's USB 2.0 port (important)
(5) Open device manager on PC and scan for hardware changes from the option if your device is not listed already
(6) If it shows 'Asus android device' -> "ASUS Android Bootloader Interface', right click on it and uninstall device with the 'delete the driver software' option ticked.
(screenshot 1 & 2)
(7) Now scan for hardware changes (magnifying glass icon)
(8) It will show 'Android' with an ! symbol
(9) Right click -> Update driver -> Browse my computer for driver software
(10) Choose "Let me pick from a list of available drivers on my computer"
(11) Choose "Android device" or "Asus android device" or similar option and confirm it with Yes or Next option
(12) A warning will pop up, press 'Yes'
(13) Go to adb folder -> shift+right-click and open cmd or powershell window -> type "fastboot devices" without the quotes and you will see your device listed.