I tried the new user account so-called solution & created a new Local Acc, (as the main problematic one was linked to my MS account). Although the new Local Acc worked fine it had NONE of my software/programs/files/settings/apps etc so was USELESS & my main
MS account was still faulty!
I then contacted MS online & after over 2 hours the best they could do was set up a new Account as my MS acc and change the faulty one to a Local acc..... this is also USELESS as NONE of my stuff is on the new MS account! This leaves me stuck using the now
Local but still FAULTY acc as I need all of the stuff on there!
Therefore I would recommend that you avoid the so-called solution of creating a new account unless you are prepared to set up everything & reinstall from scratch on the new account.
I have tried EVERYTHING suggested and NOTHING has fixed this problem since the 112015 major Windows 10 update, (before that one or other fix did solve the problems temporarily, though they soon returned).
Reinstalling Windows 10 is not an option for me and from reports I have read it isn't a solution as the faulty Start Menu/Help/Cortana & no Modern Apps working problem just reoccurs EVEN AFTER a full reinstall!
This leads to the conclusion that Windows 10 itself is the problem, (not the MS account or certain Internet Security - as people using different security packages from different companies have the identical problem). The only was I can see this being fixed
is if MS start to CARE, (unlikely),make an EFFORT to find the fault/bug and send out a solution in a Windows Update that will fix the problem whilst keeping all of the users software/apps/files/settings etc, (just as the update from Win 8.1 to 10 did).....
until then I fear we are all stuffed!