[HTC Droid DNA] coolgare:
Welp, I ended up having to find a workaround. After many attempts to get fastboot working with windows 8.1 and failing, I threw in the towel and called in Linux.

I made a bootable USB disk using a 4gb flash drive, Linux Mint Cinnamon x64 & Lili USB Creator:

http://www.linuxmint.com/download.php

http://www.linuxliveusb.com/download

Once booted into Linux Mint, I used the post from [MENTION=222205]bashar[/MENTION] from here:

http://www.xoomforums.com/forum/motorola-xoom-development/6513-ubuntu-fastboot.html

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"•First, remove any rules you already set up for your Android Device (If any), they'll be very obvious if you look in /etc/udev/rules.d/

sudo ls /etc/udev/rules.d/

•Now, open an editor for the rules at /etc/udev/rules.d/99-android.rules:

gksudo gedit /etc/udev/rules.d/99-android.rules

•Now, paste all of the rules below:

#Acer

SUBSYSTEM=="usb", SYSFS{idVendor}=="0502", MODE="0666"

#Dell

SUBSYSTEM=="usb", SYSFS{idVendor}=="413c", MODE="0666"

#Foxconn

SUBSYSTEM=="usb", SYSFS{idVendor}=="0489", MODE="0666"

#Garmin-Asus

SUBSYSTEM=="usb", SYSFS{idVendor}=="091E", MODE="0666"

#Google

SUBSYSTEM=="usb", SYSFS{idVendor}=="18d1", MODE="0666"

#HTC

SUBSYSTEM=="usb", SYSFS{idVendor}=="0bb4", MODE="0666"

#Huawei

SUBSYSTEM=="usb", SYSFS{idVendor}=="12d1", MODE="0666"

#Kyocera

SUBSYSTEM=="usb", SYSFS{idVendor}=="0482", MODE="0666"

#LG

SUBSYSTEM=="usb", SYSFS{idVendor}=="1004", MODE="0666"

#Motorola

SUBSYSTEM=="usb", SYSFS{idVendor}=="22b8", MODE="0666"

#Nvidia

SUBSYSTEM=="usb", SYSFS{idVendor}=="0955", MODE="0666"

#Pantech

SUBSYSTEM=="usb", SYSFS{idVendor}=="10A9", MODE="0666"

#Samsung

SUBSYSTEM=="usb", SYSFS{idVendor}=="04e8", MODE="0666"

#Sharp

SUBSYSTEM=="usb", SYSFS{idVendor}=="04dd", MODE="0666"

#Sony Ericsson

SUBSYSTEM=="usb", SYSFS{idVendor}=="0fce", MODE="0666"

#ZTE

SUBSYSTEM=="usb", SYSFS{idVendor}=="19D2", MODE="0666"

•Save and close the file.

•Change the file permissions:

sudo chmod a+r /etc/udev/rules.d/99-android.rules

• Now, unplug all Android Devices...

• Restart the uDev service:

sudo service udev restart

• Kill and restart adb:

adb kill-server

adb start-server

•Done... you should now be able to work with a device from almost any manufacturer. Plug your phone in to test. "

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BUT when I went to run adb, it said I did not have it installed and gave me a command to install adb (can't remember exactly what it was). I installed adb and also fastboot.

Then I plugged my phone & comp into usb and VIOLA - fastboot works!

For the heck of it, I ran through the Lili setup again and added persistant storage. Then I went through all this again and put the 4gb flash disk away somewhere safe - so that if I ever need fastboot again, it's ready to go :)

-Note: If you run into issues with fastboot command, type 'sudo ' before the command (no quotes).

Linux will also need to recognize any network connection you have on the physical machine - and you will need to connect to the internet to get adb & fastboot libs installed initially.