Vista issue?

I have installed and registered the product twice on my laptop. Both times it has stopped working and no longer appears on my task bar. It also no longer shows up as an installed program. It looks like it has uninstalled itself? Has anyone seen this??

avast never uninstall itself…
Do you have any other antivirus in this computer?
Any security program?
The icon in system tray could be removed for other programs but avast itself cannot be uninstalled by other application…
What do you get if you run:
C:\WINDOWS\system32\rundll32.exe “C:\Program Files\Alwil Software\avast4\Setup\setiface.dll”,RunSetup