I have found a solution that has worked for me
once so I can't say that it is a reliable approach. However it is consistent with a potential cause of the problem.
Many posters have suggested restarting the computer to solve this problem. I haven't waded through the 30 pages of this thread to see if I am duplicating a posted solution but what worked (again, once) for me was to do a TOTAL shutdown. See
http://windowsten.info/tutorials/5767-how-to-fully-shut-down-windows-10.
When you close Windows 8, 8.1, or 10 normally you aren't really erasing all session information. Instead, Windows is saving its internal 'state' and when you start the computer again Windows just rereads the saved state from disk and restores it. That means
if you have a problem with the Start button the problem is restored along with all of your other settings.
The link above gives the command line step to force Windows to totally shut down and not save its current operating configuration. The next time you start Windows it starts the old fashioned way, by executing a complete start up sequence and not by reading
the old session state. Note, this doesn't erase anything you have configured, it just takes a little longer to start the computer since Windows has to execute commands in its startup sequence instead of just reading the internal memory from disk and copying
it back to memory.
I suspect that some sequence of events is causing the problem. I can go months with no issues and then experience the problem again. Other posters have reported that the problem goes away when they do a Windows update which is understandable as the update
probably does a total restart of Windows. In addition, I regularly use three different accounts on the same computer and in at least one instance had the problem occur for one account but not for another.
I followed the directions in the link to create a desktop shortcut to do a total shutdown. (This is partly because I use SQL Server and this sequence also saves a step with shutting down this program.) If you don't want to create a shortcut you can right-click
Start (that seems to work all of the time), select Command Prompt, and type "shutdown /s /t 0" (without quotes).
Good luck to all of us. I'd be interested in knowing if this works for anyone else because I haven't had the problem resurface since trying this once.