Take it you have tried a Reboot/Restart of your PC
If so this mean that at least one of the avast! services are not running. See Administrative Tools > Services and check both avast! services to run automatically at boot time. Start the services as well. Then Reboot/Restart.
If this still not work, try a repair of avast, (Control Panel>Add/change programs>Avast>change>repair.)
--lee