Booting from Microserver eSATA port

I'm running a N40L microserver with bog standard BIOS. I've pulled the boot disk out from inside it, put it into an eSATA capable caddy, plugged everything in aaaannnddd... Nada. The boot disk isn't detected on startup unless I plug it in via USB. So the question is, Is the eSATA port enabled as standard and can you boot the server from a disk attached to it?

TIA

I would install the "unofficial" bios first before going any further...

While I was waiting for a response, I installed an unofficial BIOS. Unfortunately that hasn't made any difference; the external hard drive remains undetected and doesn't show up in the BIOS at all. Looks as if this may well be a cable and/ or caddy issue.