Have you rebooted since installing ?
Have (or did) you another Anti-Virus installed in this system, if so what was it and how did you get rid of it ?
Did you register it, if so then you should have been sent an email with the registration key.
If you haven't registered it - Complete the
avast! 4 Home Registration form and you will receive an email from register @ avast.com (without the spaces) with your registration key.
Or here - SSL Registration Page:
https://secure.avast.com/scripts/register.php?lang=ENG if you have registered but haven't received an email yet.
avast! icon missing - As a temporary measure until this is resolved you can create a desktop shortcut for this file C:\Program Files\Alwil Software\Avast4\ashDisp.exe (the avast icon and interface to the providers). Right click on the file and select Send To, Desktop (create shortcut). You will need to run this after each boot until the problem is resolved.
What other security based software do you have that might block new startup entries, e.g. Spybot S&D (TeaTimer), AdAware (AdWatch), SpySweeper, Spyware Doctor (StartUpGuard or OnGuard), PrevX, WinPatrol, ProcessGuard, etc. ?
Check the option in the Appearance tab of Program Settings.