One day, my Windows 10 Start and Search buttons died. This fixed it. I posted at http://home.bt.com/tech-gadgets/computing/has-your-windows-10-start-menu-stopped-working-here-are-four-ways-to-fix-it-11364000314532#disqus_threadthread
Right-click desktop. Go to Personalize/Start (5th item). Click Start Full Screen/On.
Restart . . .
Right-click desktop. Go to Personalize/Start (5th item). Click Start Full Screen/Off.
Start and Search icons both restored.
The only odd thing I've done lately is let my son copy a DVD because his Mac has no drive. He used his old Windows logon, for the first time since I upgraded to Windows 10. I wonder if that is related to this problem in some way or just coincidence. I also had a problem with the icons locking into place to the left. There is solution for that too.
This worked just fine! Thank you so much!!