Firstly the real-time protection isn't in msconfig (you will find them in the services), only the entry for the systray icon/s ashDisp.exe, this is the interface to the on-access resident scanners. What avast! processes are running in the Task Manager, they begin with ash and asw ?
avast! icon missing - As a temporary measure 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).
What other security based software do you have that might block new startup entries, e.g. Spybot S&D (TeaTimer), AdAware (AdWatch), SpySweeper, PrevX, WinPatrol, ProcessGuard, etc. ?