Hard-disk failure

If the old disk doesn't work, and neither does a new drive, there might be more to it than just a hard drive failure. I'd say beware.

 

...how quickly has it burnt out both HDD's?

I have a 10+ year old Dell Dimension 8100 desktop that burnt out 3 HDD's during the 4 year on site warranty and thankfully it hasn't roasted a drive since the warranty rant out... I chalked it up to a bad batch of HDD's at the time...

 

The 2006 MacBooks came with a particular model of Seagate drives that were notorious for failing. Mine had two of those drives fail (original and a warranty replacement). After the second warranty replacement, I decided to get a larger drive anyway, so I replaced that one with a Western Digital that's been going strong for 2 years. The third Seagate is only used infrequently as an external scratch disk when needed. I don't trust it for anything important, given the prior 2 failures.

So it's possible that the failed drives are part of this bad batch and nothing to worry about. In your case, I would try to find out if the second drive is also the same model Seagate (mine's a ST96812AS), or if that drive can be verified to work in another machine. Without this kind of information, I'd be a little wary.

If it's the computer that's bad and can't use an internal drive anymore, then at best you'd always have to run with an external Firewire or USB drive - which is cumbersome with a laptop. And from what you've said, it's not even clear to me whether they tested it with an external drive to verify that the problem isn't something else entirely?

Definitely get more information if you can.