When trying to boot from a CDrom / DVD to install Windows on a Dell PC, you get this message:
Press F1 to retry boot or F2 to enter setup
This is because you need to enable Legacy Boot and disable Secure Boot in order to install the operating system. I don’t know why this is the case for Dell PCs, I suppose disabling Secure Boot kinda makes sense because it prevents you from making changes to the boot sector of the hard drive, but I would have expected it to have just given a pop up telling you that some software is trying to install to your boot sector and as for a password.
Still, disabling Secure Boot and setting the Dell PC to use Legacy Boot gets rid of the Press F1 to retry boot or F2 message and allows you to boot from your installation media.