Can you be a little more specific ?
What errors are being displayed ?
Is the avast icon in the system tray, what avast processes are running in Task Manager (or the vista equivalent) ?
Is this a new vista system, clean install or upgrade to vista on your old system ?
If you have upgraded your existing system to vista you need to reinstall avast, uninstall, reboot, install. It would probably be best to download the latest version of avast and save it to your HDD, somewhere you can find it again. Use that when you reinstall.
