Right clik on avast! icon in sys tray, select program settings, clik on update(Basic)
and make sure your auto update is checked.
Then, if you have a firewall, go into its' allowed program settings and make sure that avast! is
allowed to connect. The program usually checks for updates as soon as your desktop boots up,
but I have noticed that if I decide to open my browser right away, it will check for updates in the background,
you should notice the icon spinning, which is a clue that the program is active and either checking your system, or checking for updates. I know that mine checks daily.
Hope this helps