When updating the OS, the better is update all avast again:
1. Download the avast! setup (current version 4.1.319). Take note of your Registration key or, if you need another key, the registration form can be found
here2. Desinstall avast (Control Panel)
3. Boot
4. Use
Avast Uninstall for complete desinstallation
5. Boot
6. Install the downloaded setup file
7. Boot
8. Enter the Registration key and configure avast! for your needs
The task names of avast should be in Windows 2000 (as in XP):
1. ashDisp.exe (Application - actually, tray icon)
2. ashMaiSv.exe (Application - Internet Mail)
3. ashserv.exe (Service)
4. aswUpdSv.exe (Service)
5. ashSimpl.exe (Skinned Application, present only if console window is open)
The first four must be running into your OS.
Happy New Year.