Try downloading the Avira Reg cleaner, available near the top right of the page
here and see if that helps.
Go to program files in windows explorer, locate the folder for Avira (if present) and delete it.
Go to documents and settings>(your logon)>Application Data (you will need to show hidden files), find the folder for Avira, and delete it.
This sort of hunting down of files can go on for a while during what has become a manual uninstall. There may be stuff lurking all over the place.