I'm not having any more problems with Avast on my Windows 10 build 10547.
Even the problems I had with Office 2013 disappeared once I ran a repair of Office 2013.
I also bypass the login screen but, when the white screen problem first appeared, using CTRL, ALT DEL.
brought me to a sign in screen except the ability to type on that screen was not possible.
Using CTRL, ALT, DEL again made the sign in possible.
Once signed in, I again used the netplwiz run command to bypass the sign in screen.
I haven't had any problems since.