Windows user not opening

[sacsac9]

So yesterday just booted up my desktop pc, and typed my password just like i do every day, ive had this pc and user for about 7 years, it used windows 7, and when 10 came out, i waited a bit and then switched, and in the process linked the user with my microsoft account, but it would still let me use my old pre windows account password without a problem. Back to yesterday, i tried to login, but the password did not work, tried to check if it was caps lock, and still nothing, i changed the microsoft account password and used that one, nothing, so i tried literally everything, there is another admin level account in that pc and i tried to change the password from there, and it wouldn´t let me, i have a lot of really important files there, what happened and how could i fix it?