[Shield Tablet Q&A, Help & Troubleshooting] howardholton:
Solved it:

Solution:

1. Register for the NVidia Developer program (I chose the gaming selection, not hardware). Takes about 30 seconds: https://developer.nvidia.com/gameworks-registered-developer-program

2. Download & unzip the Shield Software: https://developer.nvidia.com/gameworksdownload

NOTE: Make sure you download the correct version for your Tablet. WIFI, LTE-USE or LET-RoW (Rest of World). DO NOT FLASH THE WRONG ONE.

3. Download the Minimal Fastboot and ADB http://xdaforums.com/showthread.php?t=2317790

4. Install the drivers for the shield from the NV download in step 2. The one PDF in the download is instructions (ish) if you need them.

5. Run the Minimal Fastboot and ADB installer.

6. Copy the contents of the fastboot folder to the NV folder from Step 2 (this is easier than editing the path for a single use).

7. Power off the tablet and connect it via USB to your computer

8. Hold down the Volume Down button for 3 seconds, press the power button and continue holding the volume down.

9. At the recovery screen you will see a menu. Look carefully. The bootloader will need to be unlocked. If it is locked see the note below. Select fastboot and press power. (I am not sure this step is required, since it returned me to the same menu, but it worked)

10. from the NV folder in step 2, double click "flash-all.bat" to flash the tablet.

If this did not work I would imagine that your boot loader is locked.

NOTE: To unlock the bootloader (Instructions are from NVidia directly)

Your SHIELD TABLET may have shipped with a locked bootloader. To update the device,

you must unlock the bootloader using the following:

- fastboot oem unlock

- Press the "Volume Down" button to select "Unlock bootloader" option on device

- Press the "Power" button to confirm the unlock. Your device's bootloader is now unlocked.

The complete instructions from NVidia (may be easier for some)

SHIELD TABLET RECOVERY IMAGE FLASHING INSTRUCTIONS

To follow the instructions in this guide, you will need adb and fastboot.

These tools are provided as part of the Android SDK:

http://developer.android.com/sdk/index.html

Before flashing this recovery image to your SHIELD TABLET, connect your SHIELD TABLET

via USB to the PC where you downloaded this recovery image.

Next, put your SHIELD TABLET into fastboot mode using one of the following methods:

SW method:

- Boot to android home screen

- Connect the device to linux/windows system

- Open terminal (on linux); command prompt (on windows).

- Type "adb reboot bootloader" in terminal/command prompt

HW method:

- Turn off the device

- Press "Volume Down" -> "Power", hold "Volume Down" and leave Power buttons till device boots

To flash this recovery image to your SHIELD TABLET, run the following commands from

the directory where you extracted the recovery image package. If this is the

first time you have done this procedure, you must unlock the bootloader (see

below):

fastboot flash recovery recovery.img

fastboot flash boot boot.img

fastboot flash system system.img

fastboot flash userdata userdata.img

fastboot flash staging blob

fastboot flash dtb tegra124-tn8-p1761-1270-a04-e-battery.dtb