I created bootable USB flash drive using the downloaded Ubuntu 18.04.2 ISO file and Rufus. I booted up the HP Proliant. Instead of Ubuntu starting, I get a DOS message about FreeDos and the C:> prompt. The same occurs if I try to run it on my HP Laptop
Rufus developer here.
Most likely, you are seeing this because you forgot to properly select the ISO in Rufus or changed the Boot selection field to
FreeDOS after you picked the file.
You need to make sure Boot selection says something like
ubuntu-19.04-desktop-amd64.iso (or whatever the name of the ISO you selected is) before you press START. If you don't see the name of your ISO when you press START, it means that you haven't picked the proper option to create a bootable Ubuntu drive.