Hmmm... Well, it's possible that the ribbon cable could have shorted out and taken the power supply with it, or one of the motherboard components, or one of the motherboard traces. That's in order of preference, the power supply is the easiest to sort out. If this is the case though, it doesn't take all that much current to do that type of damage, and so there may not be any signs of burning or anything. This would be most likely to happen if it's the power lines that were chewed on, they're the last 4 pins (41-44) on the ribbon cable - though if you've an external PSU for the drive it could be a different problem entirely...
