Imac has shut down after softeware upgrade!!

Hello,

I have a new Imac and was updating the software after a regular auto prompt. Having clicked yes to update the Imac froze up and when I rebooted it asked me to re-register. This was worringy and having gone through all the registration process it simply asks you to register again, and again..

Has this happened to anyone else and how do I fix.

Any help would be hugely apprectiated. It was a while since my last external hard drive back up and I don't want to lose all my pics, music & vids.

Thanks,