Terminal won't accept my password when trying to use su, but works for root

okay, now I made another new account and the su command works for that one (it accepts the password), it seems it is just the broken one that it won't work for.

Yes, I was able to make a new admin account, although not from the menu since the corrupted account won't even let me open system preferences. I did the new account by starting the computer while pressing down "command" and "s" and using some code according to some guide I found online. So the new account works fine and I found a solution on this web page about how I would be able to fix the broken account from the new one (link to the description above) but this is the part where the command in terminal struggles. So now I'm stuck with a new account that works fine but I can't get access to anything in my old account.

Tried Safe Mode but the problem is still there. Both the problem with non-working programs and lost icons and being unable to use su in terminal.

Sadly no, only bothered to make back ups of pictures since I don't have that much important stuff on my computer.

Yes, tried all possible passwords (by which I mean the passwords for both the working admin account and the broken admin account) but nothing works. It only says "sorry".