If you have to use a FreeDOS USB stick, be sure to type:
C:
Doh. It starts up at A and I couldn't find the Bios file. Nobody told me that till I saw it in a YT vid.
Now I have a 9 yr old Optiplex 3010 with a 3 yr old Bios. Yea.
BTW, Optiplex Bios files start with an O, not a zero. If you type dir, you'll see that.
And to get Unetbootin to make the FreeDOS drive:
sudo add-apt-repository ppa:gezakovacs/ppa
sudo apt-get update
sudo apt-get install unetbootin