Well, I've already recovered the data off the drive. It has been doing this for the past year or so - Failure to spin up on power on, not detected by the BIOS.
However I did go to delete the partitions from the drive and was greeted promptly with a "Generic Windows Service Host Failure" error message, after which I couldn't even shut down the machine normally (ATX Power button time). After restarting, the BIOS wouldn't recognize the keyboard, which I removed all power for a few seconds, and here I am.
This is getting to be bad.