@vittau:
1) do you have any recent errors in Event Viewer? [Control Panel -> Administrative Tools -> Event Viewer -> Windows Logs -> System]
2) do you use Free/Pro or IS?
3) do you use other security apps which could be in conflict with avast? [compress tools, backups, encryption, ...]
4) do you have only NTFS partitions?
5) do you have some new files in \Windows\minidump folder?
Thanks