On my Surface Book running Win 10 (1809), I use my Microsoft account for login with Windows Hello or the Pin. The other day, I did a msconfig diagnostic startup due to performance issues. On restart and login, Windows Hello was disabled it wanted my account password - no option for the pin either. Unfortunately, despite entering my correct and current Microsoft account password (verified on another machine), the password was deemed incorrect. Selecting forgot password looped me back to a Windows Hello attempt which was still disabled from the diagnostic startup, and then it asked me for my password (no option for pin) - rinse and repeat. At that point, I had to do the power off / power on cycle a few times to force recovery mode and try a restore. Obtaining my Surface Book Bitlocker key from the Windows repository on a different machine, I typed it and then it asked me for my Microsoft account login. You guessed it, the correct password was deemed to be incorrect. Finally, I used the nuclear option to do a full reset (remove everything) to get my machine back. After the lengthy reinstallation, I tested logging with just my Microsoft account password and it worked fine. The only thing I could think of was I had changed my Microsoft password a few months ago and the Surface Book must have been looking for the old password?