Avast pro how to activate?

Hi, i had buy d avast antivirus pro, so how can i activate with the serial number?
My computer had sent to repair so all the data had gone…
I hav a installation CD of avast, but when i install, it said need to upgrade, but dunno y unable to download, d update program stop every time.
So i download from d avast website, so hw can i activate it?
when i choose register, it straight away go to d link “store.avast.com
my avast still have few month left…
please help me to solve it, thanks

you need to insert the License file you got when you bought it

avast! 8.x: Inserting the license file into avast! Pro Antivirus
http://www.avast.com/faq.php?article=AVKB8#artTitle

It sounds like the OP lost the license file, when his computer crashed. If that was the case, then follow this link:
http://www.avast.com/en-us/resend-license-paid.php

and Avast will resend the License File to the Email you put in (which should be the same one you bought it with)
Then just insert the License File into Avast the normal way.