If you look at this post (When I start the computer, it only shows the terminal), it clearly describes my actual problem. I have a computer on which ubuntu boots directly to the ubuntu terminal display and if I want to go to the BIOS by pressing F2 I have to enter a password which I don't know of.
I've tried those commands:
sudo service lightdm restart
startx
I even tried the method described in this post: https://unix.stackexchange.com/questions/616001/cant-access-to-ubuntu-interface-when-i-open-ubuntu-just-terminal-inteface
But neither of those methods worked and I'm stuck here.
Do you know which other solution there is for my problem? Or am I stuck with finding the BIOS password?
Thank you a lot everyone for your help.