What is the infected file name, where was it found e.g. (C:\windows\system32\infected-file-name.xxx) ?
Check the avast! Log Viewer (right click the avast 'a' icon), Warning section, this contains information on all avast detections. C:\Program Files\Alwil Software\Avast4\ashLogV.exe
- Ensure that you have hidden files and folders enabled and disable hide system files in Windows Explorer, Tools, Folder Options, Hidden files and folders, see image. This is for my XP Pro system, I don't know if the settings are the same or in the same locations.