Wndws 10 login problem

[Inka]

Hi, my boyfriend gave me his old computer and downloaded windows 10. The computer had 2 accounts his and mine. My account never had password. Today I tried to use computer and my account says that my password expired and that I have to change it. I never had password and I can't use the computer at all. Can this be caused by Windows 10 (perhaps expired probation prriod) or could my ex actually block me from using the computer? Sorry I am completely illiterate using pc's