not able to boot LMDE3

I have been running LMDE3 for over a year without problems on Lenovo ideapad 320. This morning at boot the system asked for my password - it is set to login automatically- and at the password, it just went back to asking for it. I have tried recovery mode, and it gives "cannot open access to consol, the root account is locked". Although I've been using various distributions of Linux for almost ten years, I am really a beginner on any manipulation; the most wonderful thing for me is that Linux hardly ever has any problems. I have no IT training at all. I'd be glad of any help with this problem, thanks!