Update: I plugged it in today to try some of the suggestions and found it wouldn't spin up at all, then the drive itself began to smoke, or rather a small chip on the logic board caught fire.

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I've encountered two instances (same brand and model of drive) recently where the spindle motor developed a shorted winding, and cooked the motor driver (releasing all of the magic smoke upon which all electronics depends). I hope this is not your problem, for swapping circuit boards does not help in this case. If it was just a spontaneous suicide, swapping boards will solve your problem. There's no simple way of knowing ahead of time, unless you can find/deduce the pinouts for your spindle motor and make a few resistance measurements.