Did you do the update through the tablets actual "Update" feature in settings? Or did you try to install it another way? If you tried the latter, that isn't the best of ideas. You may have also have gotten a bad app, malware or virus that is the cause.
Try and see if you can uninstall the update (if not done through the phones actual update feature). If that doesn't work, then try launching in "Safe Mode" and see if it will load. If it does, then you need to locate the app, virus, malware, etc., and get it off the device then restart in normal mode.
As a last resort, should none of the above work, then you may well have to do a "Hard Reset". However, as I said, this should be a last resort as it will wipe all your personal data.
To...