On-fire,

Your installation is corrupted. When you try to uninstall, you must reboot before trying a clean install.
At this point, go to www.avast.com and look up Programs…Avast Uninstall Utility.
Download and use it to remove all traces of Avast.
Reboot and then reinstall.

Have you had any other AV installed prior to Avast?
…especially Norton!

Let me know.