Ever had an apple laptop die on you? Two weeks ago I did. Lucky for me it was not a hard drive problem but some other hardware.
I am going to skip all the drama and get to the point.
If you can boot your computer in target disk mode by holding down T while rebooting, all is not lost. With either a firewire or thunderbolt cable you may be able to coax it back to the land of the living long enough to get anything you want off of it.
This is what I did. I picked up a firewire and and connected it to the bum computer. I booted it in target mode. Next I grabbed a mac mini and held down option while booting it. This gives you a chance to select a boot drive. Connect the working computer to the bum computer. In a few moments it should show up as an option to boot from.
You are now running your bum computer on the hardware of the working computer. It should work just about how it was before things took a turn for the worst.
Get what you want off of it. I would recommend not migrating all that cruft that built up on the old machine. Moving to a new machine is a chance to start new habits. I have had a bad habit of filling my desktop with files and then creating nested folders of files I should have thrown away. I also had hundreds of download files in my download folder… and a dozen other bad habits. Now is your chance to break with that and start doing things right.