You are the second person to report this specific issue recently. The OP in this thread never resolved his issue but he ignored many of the suggestions:

http://forum.avast.com/index.php?topic=149912.0

Looks like Eddy already gave you some good advice so the only thing I can add is to make sure that any “antivirus trialware” is completely uninstalled before you attempt the installation of another antivirus. Now, many of these AV providers offer a clean uninstaller (similar to aswclear offered by Avast) so make sure you take advantage of same just in case you run into some issues when installing your next antivirus solution. Good luck.