Imac computer is inaccessible and will not respond to any commands/reset requests, please help!

Hello! My sister recently somehow broke her desktop 2012 (or 2013?) iMac computer that was gifted to her by not remembering any passwords to any accounts on the computer. She doesn’t have any of her passwords written down nor has her apple id from this computer on any of her other devices somehow which is beyond me. I would love to use this computer for myself, however, it doesn’t respond to any commands given on the keyboard. I have tried factory resetting/wiping it, EVERY SINGLE kind of command I have seen from online help websites/videos, etc… it doesn’t respond to any kind of commands except for making a little sound when i try to type the commands on the keyboard. For reference the computer does not lag or seem to have any issues other than this, it also looks to be connected to the internet because the wifi symbol is full. The login screen is the only accessible part of the imac. Additionally there are not any “forgot password” buttons that show up when i repeatedly type random passwords into the enter password bar. This computer can only: turn off/on, reset, turn up/down volume, turn up/down brightness, type into the password bar, click on the login screen options (which consist of input sources, password bars, account profiles, and the three buttons at the bottom which are shut down, restart, and sleep :/. I would love to use this computer is just seems that nothing I do works for whatever reason? I would love for someone to help me, and i would like to mention one more time i have repeatedly tried to do multiple commands on my keyboard (which I know the keyboard is perfectly fine) but they do not do anything. Thnx!