There are several things you must understand if you are ever to work this out.
The first one is that your Microsoft Account password and your Windows 10 login password are not the same thing, though people very often set them up as the same thing when they adopt a given e-mail address as their Win10 and Microsoft Account login ids. Very often people start out having the same password for their e-mail address, Win10 login id, and Microsoft Account because that's what they've entered when setting up each. However, there is absolutely no synchronization between these and you must not believe that there is.
From the description you've given I am presuming that you had been running the pre-anniversary update version of Windows 10 (1511) and, for whatever reason, it was showing strictly your e-mail address on the login screen. I thought things had changed before the Anniversary Upgrade to show whatever you'd set as your "real" name for the userid in question rather than the e-mail address, but I know it changed [I'm currently doing a search of the registry to see where, exactly, it picks up that information from]. This, however, does not change the password that is used with that Win10 userid.
Changing your password on your Microsoft Account does just that, and nothing else. It does not go "in reverse" and change your Win10 login password. My password right now is one thing on my Win10 machine and my Microsoft Account even though they started out the same and are associated via the same Gmail account.
Please try the password you always used. The warning you got about changing the Microsoft Account password often comes if the association between the Win10 userid and its linked Microsoft Account somehow gets broken. That's how I ended up changing my Microsoft Account password (and I wouldn't have otherwise) but my Win10 userid password remains entirely unchanged. Just try logging in again on the computer with the password you always used, not the new one you've used on your Microsoft Account, and report back.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story