So you signed in with a Microsoft account to create your account on your computer, correct?
If so...disconnect from the internet (unplug ethernet, turn off wifi if on a laptop, etc.). Use the NT Offline Password Editor: Offline Windows Password & Registry Editor
Clear the password for your account and reboot into Windows. Should be able to log into your account. Now create a local
account, and then you should be able to take ownership of the C:\Users\<old_username> folder and copy the files off to your new local user account.