The cause of this issue may be somewhat complex.
IF Microsoft researched all users with "Start Menu" issues perhaps a common cause or trend would emerge?
As it is, hardware manufacturers provide support for in-warranty users, and out-of-warranty users are left with finding solutions for themselves.
Noted: Many here in this Microsoft community had issues with the "Start menu" much earlier than me.
Backgound for three computers (one affected):
My Dell 2013 XPS 2720 i7 desktop is affected but
not my 2014 Dell XPS 18 i5 or 2015 Dell 13 2-in-1 i7 (so far, fingers crossed). All three are under warranty; upgraded from W8.1 to W10; set to auto update; and updated from W8.1 to W10 as soon as feasible so that was some time ago. The desktop has
had some issues including blue screens, but all were resolvable with Dell Tech Support assistance until the "Start menu" and "Help button/Cortana" issues arose on
1/5/2016.
ASIDE: I keep a log book for each computer so I can reference details of all issues by date.
My loss of "Start menu" functions and a loop to restart started on 1/5/2016 (desktop only).
I found the BT UK page most helpful for suggested solutions: http://home.bt.com/tech-gadgets/computing/has-your-windows-10-start-menu-stopped-working-here-are-four-ways-to-fix-it-11364000314532
IMPORTANT SUGGESTION: One issue that Microsoft needs to resolve NOW is to bring back error codes.
IF users had error codes, we (and support technicians from other computer companies and service providers) could find help and suggestions on Windows Support.