[Bookerv12]

Hi,
We just went through this, except with a few more symptoms.
I did the harness on a couple of others, and found that it was not the harness, but oxidation on the male pins that the harness attaches to.
Take the top off, gently pull off the 3 harness connections. (You'll need to pry the clip with a little screw driver)
Spray/coat the pins with Deoxit and use either fine sandpaper or a pencil eraser to burnish the pins.
Pop the harness back on.

Now that you know that you are starting from step one, if the machine still misbehaves, change to a new, high quality Firewire cable. (Not Best Buy or RadioShack, Trust me.)

That should get you back up and running.

We had a Firewire cable go bad for no reason yesterday.