Not on the avast site they only support current versions, there are various download resources that retain old versions like filehippo.com - http://filehippo.com/download_avast_antivirus/, on the right of the page there are earlier versions.

It is strange if there is no activity, but CPU usage and the tray icon isn’t rotating. Normally I would suggest an avast Repair, but you say you have done a clean reinstall. I would still give it a try first before going back to an older version.