This problem is extremely annoying: sometimes, the Start menu in Windows 10 will outright stop working. It won't appear when the Start button is clicked or the Windows Key is pressed. In addition, various Windows 10-style windows (such as the system's volume control that appears in the top-left of the screen when the volume is changed) will also not appear. Right-clicking on the Start button will then cause any 10-style windows to then draw... it's all very weird.
After many months, it seems I may have stumbled upon a fix for the issue. Every time I tried restarting or shutting down the system, Windows always complained about there being a task that wouldn't exit. The string given is:
Microsoft\windows\plug and play\device install reboot required
Microsoft introduced a "feature" that allows Windows to finish installing device drivers after an update or restart. Awesomely - it doesn't work. This broken feature has been the cause of months of (random) frustration and re-installations.
Anyway - whatever, onto the fix. Hopefully it's the fix; I haven't ran into the Start issue since.
To do this using the Start menu (eg. you're performing this as a preventative measure), just type
Settings into the Start menu and open the item that appears.
If you have a broken Start menu, you can either click on this link right here or press Windows Key+R to open the Run window and then type the following, followed by pressing the Enter key.
Include the trailing colon character otherwise you'll get an error.
Settings window that appears, click on
Accounts (the little round guy; second row in the second column in my particular version).
On the left, click on
Scroll down in the view on the right and under the
Privacy heading, uncheck the Use my sign-in info to automatically finish setting up my device after an update or restart.
That should be it.