I had the same problem and figured out a solution.
In my case, I created a Microsoft account for my windows phone and later, when I tried to login in to my laptop, it said the password was incorrect. After losing my mind and spending hours researching the problem, I noticed that in the bottom left hand corner of my login screen showed two names: "Susan" and "Default", which I had never noticed before.
I clicked on "Default" (instead of "Susan" which was selected) and my regular login password worked. My laptop is not synced with my PC or phone so I'm not sure how a new Microsoft login was created on my laptop. I'm just happy I'm now logged in.
So frustrating! I'm going to log out of all my microsoft accounts before I find myself locked out of another device.