It also says
this application has failed to start because aswCmnOS.dll was not found. re-installing the application may fix this.
can any one help i want to un-install Avast completley and re install later.
Which is your Windows? 98, Me, XP, Vista?
Do you use any other antivirus in your computer?
Can you try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove. Then choose Repair function in the popup window (Repair).
Will this help? http://forum.avast.com/index.php?topic=31412.msg261499#msg261499