Not long after I installed avast and becoming registered my computer crashed, looking at the email that was sent to install in the first place, it doesn’t tell me how to re-install now that my computer is up and running again, if I can’t re-install it’s been a waste of money…
It sounds like you have the original e-mail sent to you with the registration key.
Download the latest version, install and insert the key.
As oldman says download the program again, http://www.avast.com/eng/download-avast-professional.html, install and enter the registration key again.
It would also be helpful to know what error message(s) you got when the computer crashed.
There was no messages, the computer just got to the welcome page and just re-booted, just wouldn’t stop re-booting.