I have a Lenovo desktop i7 that I bought back in Dec 2013. Best PC I've ever had. It runs Xubuntu Linux long-term support. Yesterday I moved, and for the first time in six years, that PC was powered off for an extended amount of time.

I hooked everything up this afternoon, and when I turned it on, it didn't load the GUI. It wanted me to log into a terminal session as root. I have a couple of external USB drives that are mapped in /etc/fstab, and they weren't plugged in when I'd started the PC. I powered it off, plugged in those drives, and when I restarted the machine the BIOS gave me a cryptic message suggesting I remove any drives that were interfering with booting and try again. I went into the BIOS, and it showed both my SSD and HDD and the SSD was set as the first device as it should be.

I went to my laptop, downloaded the latest Xubuntu .iso, and wrote it to a thumb drive. I confirmed on the laptop that the thumb drive worked. I plugged it into my desktop, went into the BIOS, and it was there. I set it as the first boot device and rebooted. Then I got the same cryptic message from the BIOS regarding removing drives. FWIW, both of my external USB drives were disconnected at this point.

I think my Lenovo is dead. Just asking if there's anything obvious that I've missed.

Thanks

Back up fstab, remove external drives from fstab leaving only OS install drive in fstab, reboot? If it doesn't work you can always revert and try something else.

I got to my OS on my first boot of the day (but no GUI).

Now I can't access fstab because I can't boot to an OS. No matter what I choose as my first boot device in the BIOS, I get this weird error message about removing drives that are interfering with booting. The message is from the BIOS. It's not accessing my SSD. It isn't getting that far in the boot process. I tried a live OS, but I couldn't boot to the thumb drive. Got the same error message.

Have you tried disconnecting all drives and booting off the thumb drive?
Have you tried replaced the CMOS battery?
Have you tried reseting the bios?

If it's not booting or trying to boot - it's far likely that it's trying to boot the wrong drive.

CMOS matters on boot order (correct drive)
Check cables since you "moved it".