Power down

Please excuse the simple question, but it's something that's been bothering me. I've been running various debian machines as servers for quite some time now. The problem started when I got two new servers. All of the other machines (excluding the two new ones) were on the older side ( <= P2 ). The problem is that when I shut down the servers.. they don't turn off. It's particularly irritating to me because all of my servers run headless. With my older machines, I never gave a second thought to the shut down process as they'd always turn themselves off as soon they finished wrapping things up. The new ones just halt and stay on. To make things even worse.. the hard drives in the new machines are so quiet I can't tell if they've finished everything.

Anyway, does this have something to do with newer power management stuff in the bios? Something changed in the debian configs? All i'd like is for the servers to turn themselves off at system halt like my old servers do.