Locked out of Ubuntu 20.04

[kalpana]

Hi,
I am no longer able to access the Ubuntu 20.04 OS -- desktop -- on a Lenovo x230i, on which I am writing a book.

On Friday, something went wrong while typing in the two passwords I need to transition to my Ubuntu 20.04 files.

Instead of getting the Ubuntu log in screen, there now just is a black screen with a blinking cursor in the upper left corner.

Today, I tried another internal disk on this laptop, after installing another Ubuntu OS -- with some difficulty. Now I only have to type in the initial password -- not two passwords -- before the Ubuntu log in screen comes up.

However, I would really like to continue working on the former internal disk and wonder how I can call up the Ubuntu 20.04 log in screen again.

Suggestions welcome.

P S this is a different Lenovo from the Lenovo x230 discussed in another thread....