Well, I did a full system restore from 3/20 using EaseUs Backup. Wasn't expected it to fix my original problem as I had already restored windows restore points back to 3/18 or so. That put me back at my original problem where my user didn't show up in windows. At this point I used net user to see what groups that user belonged to. It only belonged to HomeUsers, which seemed strange as it was an Administrator user. So, I added it to the Administrators group using net localgroup and what do you know I can login as that user again. Didn't have much time to test it this morning before work, but initially it looks fine.
So for some reason Windows removed that group from my user, and only being in HomeUsers doesn't allow windows to see it at login or in control panel add/remove user. What is the HomeUsers group for? Do I need to be in it? My backup user isn't in it. The one thing I did to my user before all this was add my Full Name to my user as it was never filled out. Maybe when it wrote that information into my user it dropped the Administrator group.
As for why copying my user to another user caused windows to go craze, I don't know for sure. My theory is some important files that got moved to the new user from the old user still referenced my original user, and because it didn't belong to Users or Administrators it wasn't allowed to run things like explorer.exe. I don't know what files would cause that behavior though or how setting the default media play and browser triggered it. I assume it caused windows to re-read said files, and that caused references to the original user.