As a result of Avast free causing problems on another computer (started another thread for that so won’t go into it here), I un-installed from my main one (which has been problem free).
After trying a few other AV, I have decided I would rather stick with Avast so am planning on re-installing it.
The thing is, do I have to register again or is there some way to use the existing registration?
I don’t recall getting an email with a verification code or anything so not sure what I would need.
Yes you have to register it again, you don’t need to get an email as the registration is dome from the user interface, avastUI, Maintenance, Registration.
One of the main things is to download avast and save it to your hard disk, then uninstall your current AV and reboot before installing avast.
Some AVs may need other tools to completely remove them as add remove programs, uninstall sometimes leaves remnants. You don’t say what AVs you tried, but this site has removal tools for many security applications should you need them, http://thewebatom.net/uninstallers/security-software/.