i'm having the same problem
Do you mean that you're not seeing the icon on system tray?
If so...
1. Check the option in the Appearance tab of settings.
or
2. Repair your avast installation through Control Panel.
or
3. Make a link to ashdisp.exe in your startup folder
or
4. Add the path to ashDisp.exe into a value named avast! in the Windows Registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
See picture here:
http://forum.avast.com/index.php?topic=26155.msg213891#msg213891If that does not help, please, uninstall, boot, install again, boot.
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), PrevX, WinPatrol, ProcessGuard, etc.?