Useless after Kitkat update

Hi Everyone
I updated my Nexus 7 (2012) this morning. When it rebooted, it wouldn't go beyond the 'working' four circles logo. I followed some instructions and reinstalled the update. This time it seemed to work and got as far as the choice of keyboard language. I selected 'UK' and clicked next. This brought up the wifi network selection. I chose the home one and entered the password. It states there is a 'authentication problem'. I can't go anywhere from there. There is no other option. I can press the 'back' button and go back to the keyboard choice but nothing else is available. Plus, now I don't even have clockwork recovery. It just goes back to the normal android boot. Now my laptop doesn't even see the tablet. Its driving me mad!

 

Thanks for replying.
Nope. It never recognises it. I get a 'bong' when the N7 starts and ends but when I use Nexus Tools, it doesn't see it as being connected.