What version did you upgrade from? There is a specific required path in order to have successful upgrades (it's in the Release Notes as well as a KB article). If you followed the correct path,
Try to SSH into the ZD using Putty or similar SSH client - if that works, re-boot it from the CLI (>reboot )
If that doesn't work, wait at least 30minutes then power-cycle the ZD
It may be in rescue mode - https://support.ruckuswireless.com/an...
If it still fails, contact support to open a case.