Latest update failed (4.3 to 4.4.2 I think) – just a forever spinning Nexus logo. Overwrote the tablet with a stock Nexus 7 (nakasi) image and all is well, besides needing to reconfigure everything and put my files back on it (thankfully Moon Reader Pro syncs positions with Dropbox/Google Drive).
You need the Android SDK installed (remember to add it to your path) and to have rooted the device – both covered in an earlier post. On the device hold down the power, volume up and down keys until the rescue screen appears.
Connect with USB and open a command prompt/terminal then type:
adb reboot bootloader
Download a stock image from Google – the Nexus 7 (nakasi) is this one. Decompress it and go to that folder in the command prompt/terminal, run either flash-all.bat (Windows) or flash-all.sh (Linux) and follow the prompts.