Cannot sign into iMac

For some reason, settings have changed and I cannot sign into my computer. There is also a text box on the bottom left in which I have no idea where it came from.

When typing in the password I’ve used (with minor alterations) for the past 10 years, it says it is incorrect. No idea why.

anyway, as I enter in every version of the password I’ve ever used, it provides an option to utilize my Apple ID to change the password. Great right? Easy solution!

Not really. After I do this, it takes me back to the login screen. Nothing happens. I still can’t login to use my own computer. Please somebody tell me I’m just special and or getting old.