BIOS refusing to boot a hard drive? See if it's disabled

Today I looked at a computer that wouldn't boot: it said there were no bootable drives, even though I was sure the drive in it had an OS. I swapped out the drive to another bootable one and got the same problem. I poked around a bit and ended up in the BIOS settings, where I found a section that allows individual SATA positions to be enabled or disabled. (It was a Dell BIOS, and I believe the specific settings were in the Drives section.) Apparently, someone had disabled all the positions, and therefore the computer found no drives to boot. I enabled all of them, which produced some warnings about there not being drives in the extra four positions, but it booted anyway.