Reset password or reinstall Ubuntu without access to the bios
I've had 20.04 on my old computer, that died, so I just bought a new computer. It has Nvidia hardware and had Windows 10. Of course I wanted to install Ubuntu, and instead of the LTS I chose the 21.04. It was not a dual boot, by the way. Installation went great, but then the password doesn't work.
I'd like to reset the password or even to reinstall Ubuntu as I still have the usb drive, but the computer doesn't boot to the usb on restart or even after shut down + start. I tried every advised button to open the bios (shift, escape, suppr, F1, F2, F10, F12), at the same time as I click on shut down or restart, keeping it pushed while it shuts down or restarts, start pressing when it boots, when the logo appears, and I even tried both keeping it pressed and pressing it like crazy until the login screen appears. No bios or grub.
Or, rather... I have grub when I use shift, but it's the minimal bash version, and I don't know what to do from here to boot from the usb or do anything else that would help my situation. In this console, I tried several things that I've seen online but to no avail neither. Don't ask what I've tried because I don't remember, my brain is burning, sorry. What I can say is that it probably didn't do anything because I kept receiving stuff like "this thing doesn't exist".
I've heard that the password issue may be caused by Nvidia, which is why I specified it earlier. I must also note that I've managed at some point to enter tty1 I don't remember how, but it asked for my login and password so I couldn't log in. Maybe the issue with the password is my own fault, I misstyped it or something when setting it, but now I can't use the computer at all.
Thank you very much for your help!