Hello ageo2013! What previous antivirus software did you have? Which version of avast do u have? Version 8 or 9?
Here’s what I suggest to you? If your previous antivirus was not avast run it’s uninstall utility? If u had avast 8, run avast uninstall utility http://www.avast.com/uninstall-utility in safe mode and install a fresh copy of avast 9.