UEFI vs BIOS
 

It looks like the UEFI on this machine will not let me boot from either
a USB drive or from the optical drive!

And there's no place in the UEFI to change this.

If I change from UEFI to BIOS,

1) will it hurt anything?
2) can I change back without hurting anything?

The HD is only 1/2 GB so I'm not concerned about large HDs.