Is the avast antivirus service running? If not, is it possible to start it manually? Control Panel -> Administrative Tools -> Services.
The most common reason for this is that the credentials you've supplied to the setup program were not correct (e.g. incorrect password). In that case, the service would fail to start due to a logon failure (you'd get this message from the Services applet after trying to start it manually). To remedy the situation, you'd open the service properties, Log On tab, and make appropriate changes.
Thanks
Vlk