The saga continues.

While waiting for a replacement motherboard for my Lenovo T5, I hauled out a computer I had taken out of service about 16 months ago to have a working machine until I finally can install the motherboard.  But here's the thing.  When it boots up, I can use the keyboard and mouse at the BIOS screen and through most of the process -- but near the end, after enabling the network fails, it loses the keyboard.  The mouse stays connected.  So I get a login screen but no way to talk to it.  Same problem using other keyboards.  Eventually I figured out how to boot from a USB stick, and that gets all the way up with the keyboard, so it's something odd in the setup on the computer itself.  I haven't tried to ssh in, because at the moment it tries to boot into a static ethernet address which isn't available, and so network connectivity fails.

The system runs Arch Linux.  The "easy" thing to do is just re-install Arch and start with a clean slate, which is likely what I'll do, but if anyone knows a quick and dirty fix I'd at least be able to save some configuration information from the computer.  (Yes, I can do that from an Arch install USB by mounting / chrooting into it, but I'd rather understand the problem first.)

Any idea what gives?  Obviously a module for running the keyboard isn't being loaded somewhere...