What avast processes are running in Task Manager, they begin with ash or asw, see image ?
avast starts automatically, the desktop shortcut is to start the avast processes, do a memory scan and open the Simple User Interface to run an ‘on-demand’ scan. This is only necessary if you have booted into safe mode as avast doesn’t start in safe mode. So effectively you shouldn’t have to use this shortcut.
This is a common issue with the Windows Security Center stuffing up.
Try this - Windows XP SP2, SP3:
Start, Run, type cmd and click OK from the command prompt type
‘rundll32 wbemupgd, RepairWMISetup’ without the quotes and enter.