What is your OS?
What other security software do you have or “ever” had and how was it uninstalled? Did you run a cleaner after uninstalling your previous av I recommend CCleaner http://filehippo.com/download_ccleaner/
Any previous security software could leave something behind that could affect the avast install.
I don’t see any need to “re-download” as the installation file remains the same. And besides it is always better to download before removing any anti-virus. The reason for this is that there is very little delay in getting avast up and running. :slight_smile: