unable to do any kind of live install on old dell R200's

This is kind of an odd problem I've been working on the last few months.  Note that last summer (2023), I installed Ubuntu 22.04 on all my Dell R200 servers using a usb flash drive with the relevant Ubuntu installer.  However, when I went to install 24.04 on them (this is a set of approximately 15 servers we use for assorted university student projects) it was a complete no go:

1) I could not install via PXEBOOT (it stalls at the cloud-init point and will NOT advance from there)

2) I could not install via usb boot disk (I took care to find a usb 2.0 stick in case that mattered).  Doesn't matter what I do, it drops me into grub_rescue and only shows iso9660 filesystems so I can't even set initrd/vmlinuz manually at this point. I used both disk-creator and unetbootin, it made no difference

3) I could not install from CD's -- even using boot mode, it simply ignored the CD and went straight to the hard disk. I verified that they could read the CDs once boot to 22.04 finished

Note that for each of these three methods, my non R200 servers (including a set of Dell R300 servers) were able to install 24.04 with no issues.

I then checked whether I could install 22.04-- and ran into the same problem.  It's kind of like something timed out on all of them at the same time to refuse to recognize the live installation process? 

I finally updated them through do-release-upgrade when that became available last week.  But I'm curious if anyone has an idea of what's going on here?  Ultimately, since these are our oldest servers, I will probably retire/surplus them sooner rather than later, but it BUGS me that I have no idea what's going on unless it's some kind of bios bug?

I appreciate any insights.  I realize these servers are so old as to basically be zombies but they provide useful hands on bare-metal learning experiences for our students.