[stomachmonkey]

Folder/Question mark at boot means it lost the startup drive.

Does not always mean the drive is dead, just forgot where it is. Or the drive could be dead.

They take 2.5 SATA laptop HD's so if you have a spare sitting around slap it in and see if you can reinstall the OS.

Since you have other Minis try the Target Disc mode thing.

Firewire 800 cable to one of the other boxes.

Boot bad box holding T key.

It will pop up on the other device as a HD.

You can run disk repair/utilities from the host.

If it pops up as needing to be initialized then something went bad with the drive.

If it does not show up at all then drive or whole box is dead.

If you want you can open it up and disconnect the optical drive and see if it boots.

Rare but since the optical drive is a priority in the boot sequence if it's bad it could prevent the HD from being seen.