I have recently had to reformat my computer but managed to save a handful of my programs, including ZBrush.
Whenever I try to run it however it says to reinstall it or contact Pixologic.
I have however lost the product key. What should I do?
You need to submit a support ticket at http://support.pixologic.com so that your account can be located and your activation info resent to you. While you’re there you should also register on the site. If you put your ZBrush account info into your Support account you’ll be able to access it at any time even if you lose the email copy.