You could have a troubled original hard drive and a power supply with "issues".
Or maybe you should run wdidle3 on that 10EVDS so that it hasn't already booted and gone to sleep by the time the TiVo gets organized enough to call on it.
Or maybe it's just a plague of gremlins. Been cursed by any witches lately?
You could, after undoing intellipark, try running that WD off of a computer's power supply to see if the TiVo's power supply is able to power the motherboard but not the drive.