There are a few steps that are usually needed that you didn't list. You may have done them, but I figure I better check.
1) Your phone must be in developer mode. This is achieved by going to Settings >> About Phone >> and tapping the Build Number item 5 or 10 times (you will see a notification that developer mode is active).
2) You must go into developer mode and check the "Enable USB Debugging" menu. After that, you can plug in your phone (while powered on) and after a few seconds you should see a notification on your phone asking for confirmation to allow debugging from the computer.
3)The "fastboot" command only works from the bootloader screen. "adb" is the tool you can use when the phone is on with debugging enabled. You can run "adb reboot-bootloader" and should be able to use fastboot from there.
1) Your phone must be in developer mode. This is achieved by going to Settings >> About Phone >> and tapping the Build Number item 5 or 10 times (you will see a notification that developer mode is active).
2) You must go into developer mode and check the "Enable USB Debugging" menu. After that, you can plug in your phone (while powered on) and after a few seconds you should see a notification on your phone asking for confirmation to allow debugging from the computer.
3)The "fastboot" command only works from the bootloader screen. "adb" is the tool you can use when the phone is on with debugging enabled. You can run "adb reboot-bootloader" and should be able to use fastboot from there.