So, I guess you haven't removed the virus.
You need to do this, otherwise Avast will, of course, remain disabled.
There aren't that many viruses that can disable Avast if Avast was installed before the virus, but I think there are a few. I know of a variant of the Bagle worm that reportedly can.
Please advise your operating system (including service pack), specs, and what other security you have, either installed now or in the past.
Please advise the name of the virus, as identified by a scanner, and/or original filename and path, if you remember this or have access to a log.
Try [urlhttp://www.freedrweb.com/cureit/]Cureit[/url], by DrWeb, a standalone virus scanner.
