I had to uninstall my downloaded Pro 4 version to satisfy Hewlett Packard that it wasn’t causing a conflict with my printer. I now need to reinstall it, but the current version I downloaded doesn’t recognize my product key number. This was the version that my order directed me to go to for the initial download after purchase.I could use some help.
Are you sure you have downloaded avast 4.8 and not avast 5 ?
Try download from here http://www.avast.com/download-software#tab3
If you have 5.0 installed now it is easier to convert your old 4.8 pro license - avast! 5 Pro license convert from 4.8 Pro license. Try http://www.avast.com/resend-license.php now, fill in the form giving your email and 4.8 Pro License key and they will send the new license file to you (presumably it will check you have a legit 4.8 Pro license first).
How to register avast 5 pro on page 7 - 8
http://www.avast.com/documentation/quick-start-guide-pro-en-ww.pdf also see http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=459.