Last time this happened to me it was due to an issue with my keyboard. One of my keys was not making contact as it was sticking from some dried coffee that had dripped onto the keys.
Slowly type in your password and make sure you are seeing the asterisk key ( * ) appearing after each press?
Second, use the Restart option from your computer, not Shutdown to reboot. This will force a clean reboot. What many don't realize is that WIN 10 does not necessarily do a clean reboot from Shutdown. It saves some settings to speed up the reboot process, which can cause problems if there were some corruption issues from the previous session.
It that doesn't work, your sign-in could have been corrupted from some recent update. In this case, you need to 'Restart while holding Shift key', selecting Options and reboot into 'Safe Mode with Networking'. See if your password works. If it does, just reboot and your password should work.