Angels have the Phone Box
Hi Freddel and welcome to Tenforums.
That's odd. You don't have any Microsoft account which someone may have signed in to, changing the computer's local account to an MS account? (of course, this would also change the username you see at login.)
If you have System Restore turned on, you could try restoring to a point in time before this happened.
If no restore points exist, you could turn on the hidden administrator account, and remove the password from your user account that way. Since you can't get into your account, you'd need to accomplish this using Option #4 in the tutorial.