It sounds like the drive itself is just dead. Reading your original post on this I was hoping that hooking the drive up to another computer as a secondary would let you get your data, but it looks like that failed as well. It could still be recovered, but I shudder to think what the service would cost at this point.
If you haven't already gotten it done, I can set up to have a replacement hard drive shipped out to you. If I found the correct Inspiron 8600 in our system then you still have about 10 months left on your warranty. I would just need the service tag and address to send the drive to (to verify I have the correct info). You can email that to me at email@example.com (with 'ATTN: Larry' in the subject line to make sure it gets to me).
From my experience the 8600 is a fairly reliable system, so I'm a little surprised you've had two hard drives fail in the same way. Since it looks like you had two identical drives I am going to try to have a different brand sent out in case that makes a difference on how long it lasts.
If you have any questions about this I will be more than happy to answer them.
Dell Customer Advocate
I've emailed Larry back and we shall see what we will see.
Now I want to know how he found the post. It has to be some sort of series of word searches through LJ or web or something.