HP DC5100 won't boot from DVD-ROM Drive

[Rocker4Hire]

My HP DC5100 won't boot from DVD-ROM Drive

 

[Rocker4Hire]

Background and Solution: I wanted to install Ubuntu over Windows 7 on this older HP DC5100 workstation and ran into issues with trying to get the machine to boot from the DVD drive. All of the obvious BIOS settings have already been adjusted to force the boot from a CD or DVD device. After some hardware juggling, I found the solution to my problem.
The HP DC5100 only has 2 SATA ports and 1 IDE port. I had 2 SATA hard drives each connected to the SATA ports and an "older" DVD drive connected to the IDE port. No matter what I swapped, the PC wouldn't boot from the IDE DVD drive. I had to unplug the non-OS hard drive from the SATA port 2, replace the IDE DVD drive with a SATA DVD drive, plug the SATA DVD into SATA port 2, and boom! It booted from the SATA DVD drive! I don't have a technical answer for how and why this worked but it did. My only guess is that Windows 7-8 and newer Ubuntu OS's are assuming that your DVD-ROM drive is SATA and not IDE. I just wanted to post this in case anyone else runs into this issue.