Missing the external drive that it booted from to install RHEL!

Hi all,

I have a brand new laptop that I'n trying to install RHEL 7.5 on.

At the moment, I managed to bring up the graphical install screen with the following commands at the GRUB menu: nomodeset acpi=off

This means that I now have graphical UI for the install bit.

However, the system cannot locate the install files from the external DVD-ROM or the Flash USB stick that i have used to boot the laptop with. As in this option is not available to select my iso from!!

Can anyone explain why the external DVD-ROM has suddenly "disappeared"?

Any ideas as to why the system is not seeing my mounted external DVD-ROM or my flash disk for the install?

The laptop is brand new and fairly new to RHEL.

Thank you.
Phil.