What a mess of a topic.
Almost no post is relevant to the main problem, except the real technical questions about the system. Even the first post is useless (as it has nothing to do with the problem).
Since the system with the problem is on a home computer for home - only use (at least this is what I understood), avast Free is perfectly legal on *that* system.
About other security tools mentioned, that are currently installed, I would suggest first uninstalling them. There is no "logic" on installing "extra" security tools, add on, plug in... before taking care of installing the most basic security tool: antivirus. So uninstall all those others (and after avast is working correctly, try again with them or with alternative ones that will work with avast with no conflicts).
About the pre-install security tools (like the Norton one you mention that you already uninstalled), you should use the specific relevant removal utility for the specific security tool so to remove any potential remnants. Partial list (including some norton removal utilities) is located at
http://singularlabs.com/uninstallers/security-software/. Follow the relevant info and instructions, download the relevant utility and run it accordingly so to remove the potential conflicts.
About avast, uninstall it and then run the removal utility for it following the relevant instructions, just as with the above paragraph.
Now download Windows Updates and apply them. Reboot and check for new Windows updates again. Repeat until no new updates are found. The updates should include all available SP at least (but it is recommended to apply almost all the updates, unless there is some specific known reason not to do it).
Validate / activate the OS. Then check again for new Windows Updates, and recheck the activation / validation of the OS (as some updates may undo the validation / activation).
Finally download avast Free 6.0.1367 ANEW and install a new clean installation, and reboot. Test it. If it works, go on with other additional security tools relevant to this particular system and test them too.
To summarize: a clean system, with the pre-install "crap" uninstalled and "removed", and all Windows Updates applied, should not have a problem installing avast.