The PC that says "no Operating System Found" is not set up correctly in BIOS to boot from USB (maybe you have to disable "Secureboot").
The other PC, where you only have a black screen... how long did you wait? My experience is, that on some systems you have to wait for 10-25 Minutes for the first boot of Batocera. So maybe you have to wait a bit longer.
And last but not least: Can you list the components of your PCs? Maybe they are not compatible with Batocera.