Maybe you can you schedule a boot-time scanning from Safe Mode:
Start avast! > Right click the skin > Schedule a boot-time scanning.
Select for scanning archives.
Boot.
If infected files are found, it’s safer to send them to Chest instead of deleting them.
This way you can further analysis them.
Or just run:
C:\Program Files\ALWIL Software\Avast4\sched.exe /A:“*” /archives