Well, that’s it… most likely you cleaned that virus from your computer, but also some very important system files. Probably they were damaged anyway…

If you can, backup all important data you may have on that computer (if any), and my suggestion is nice and clean reinstall of Windows.

However if you find it as too much work to do, you may try with Windows 98 repairing procedure.

See here:
http://www.helpwithwindows.com/windows98/start-142.html

Some additional information on how to do it, you’ll have to search in some Windows related forums, because this is not an avast! issue, this is Windows repair issue. Have your original Windows 98 installation CD ready, because you will need it if you decide to proceed with repairing…