Also See: For Many Nvidia SHIELD users, the Recent Update Ruined their SHIELD Experience
Here is an exceptional tutorial with step-by-step instructions on how to restore a non-responsive NVIDIA SHIELD and breathe new life into it. In order for it to work, your SHIELD must boot up at least to where it shows the NVIDIA logo. If you see the logo, you are in luck and Continue reading at slothparidise.com
USE WITH CAUTION. Using the wrong image can brick a working SHIELD.
You can find SHIELD Recovery Images here