You can’t take three from two,
Two is less than three,
So you look at the four in the tens place.
Now that’s really four tens,
So you make it three tens,
Regroup, and you change a ten to ten ones,
And you add them to the two and get twelve,
And you take away three, that’s nine.
Is that clear?
Boot problems are really tricky to fix on the computer that’s having them.
If any of your other OS’s still boot, then use them to download a live ISO of your preferred linux distro, and write it to a USB stick.
Then you can diagnose the problem using a new boot environment that doesn’t rely on the main disk.