Hi, welcome to the forum.
Your problem is that you have two AV's installed. This will cause problems, sooner or later. Possibly big problems, especially likely if they start a tussle over an actual virus.
My recommendation is to uninstall one of them, preferably Norton, and run the appropriate removal tool.
Here is a link to the Norton Removal Tool.
And, so as not to appear biased,
Here is the link for the Avast uninstall utility.
In my experience with friends' computers, Norton (especially Norton360) can do a real number on Windows updates.
I've used Norton before. It came pre-installed. Haven't had a problem since using Avast.
Let us know how you get on. Further actions may be indicated after you've removed the AV, if Windows update still doesn't work.