Welcome to Fedora @gorjes
This you can change easy when you have a sudo/wheel user.
sudo passwd root #follow the instructions
# To lock the root user again.
sudo passwd root -d
I could reproduce your error, alias when I switched fast-boot on on my older computer I just got a white cursor on the top left screen while not much happened. The computer is from 2013 and the hard-drive is a bit younger. Booting with the external disk worked. So I could enter into the bios and switch fast-boot off.
I saw your first topic in Spanish and think you should decide for the English section. You have better chances to get help because of the bigger audience here. From the topic it seams to be a duplicated request. Please consider to delete the Spanish topic.