The red light came on a few times while it was powering up, but only the green was on when it was done.
I'm not quite sure what to try next. I've disconnected and reconnected, powered down and back up again. I could take it out of the case (it is just taped in there) and plug it in to my new HD caddy, or the old one depending on the connectors.
Is there diagnostic software out there that anyone has used? Is there something built into Windows Vista?
Ah well, at least it doesn't really affect my computer.
EDIT: OK, I've remembered about chkdsk and verified that that still exists in Vista. I've also found some things to try, like going into the system to make sure the drive has a letter assigned to it. Lets see if I can get it to recognize the drive before I take it apart.