This is the first time I've tried to install a new OS with my current desktop. I created a bootable USB for Ubuntu 18.04 with Rufus (both with and without bad block checks) and attempted to boot into it through BIOS/Boot Manager, but received this error every time.
The only idea I have is that I tried to find the option to disable secure boot in the BIOS, but I couldn't find that option for my specific BIOS; I also made sure that the OS type was set to "Other OS" (other option was Windows 8). I've never run into issues booting into bootable USBs before though, and typically I don't need to disable secure boot to at least get to the installation.
The BIOS I have is a 2013 American Megatrends, I can provide other information if you ask (and if it's not trivial to find that information, please provide instruction).
EDIT: Tried again with a different USB stick, same errors. Tried to run the "check disc for errors" option within the Ubuntu boot menu, but then got the same error. Tried the same USB stick on my laptop and it worked fine, I was able to test Ubuntu and install (I didn't install, since I have no need on that computer).