How do I login when it says my correct password is incorrect?

Hello,

I have a PC I built a few years back with a legal version of widnows 7 I purchased, and I upgraded to windows 10 smoothly when it was made available for free. Recently, out of the blue, my PC said my password was incorrect when I tried to login, even though I am 100% positive it was not, and I have never changed it. I have followed dozens of online threads I read but nothing seems to be working. I went to use my computer like normal the other day, and it told me my password was incorrect. I went online to reset it, and it told me my account did not exist under the email my PC was telling me my account was. I created an account with that name because I thought maybe it somehow got deleted, and I setup a new password. When I try to login with my PC with that new password, it says something along the lines of “Login with previous system password,” so it recognizes that the new account has this password. I just did a system restore, and before that tried to boot safemode with CMD, and for both processes it had me type my password in, and my OLD password worked, despite not working on my login screen. Before this I tried going into my registry from CMD and adding a local user: did not work, I tried restoring to a previous restore point: didn’t work, and now doing a reinstall of windows has not worked. Is there any hope of me getting back into my PC?

Thank you.