OP:
Yours is a non-retina MacBook Pro, is this a correct assumption?
It's -possible- that the drive is still ok, but that you have a problem with the very thin ribbon cable that connects the drive to the motherboard. Others have reported this component as being troublesome in the non-retina MacBooks.
My suggestion as to what you should do next:
You will need a couple of tools:
- Phillips #00 screwdriver
- TORX T-6 driver
You can find these at hardware stores, Home Depot, Lowe's, etc. for not much money.
I recommend that you go to ifixit.com and check out the guide for removal of the hard drive.
I would first take the back off, then GENTLY check the connections between the drive and the ribbon cable. Put the back on again, and try a reboot. Does anything change?
If "no", here's what you might try next:
Take the drive OUT of of the MacBook, and try connecting it to another computer using either:
- an external USB3 enclosure
- a USB3/SATA docking station
- a USB3/SATA "dongle" type adapter
(any of the above will run you $20 or a little more at amazon)
Does anything change?
(If the drive ribbon cable was defective, I sense that target disk mode wouldn't help)
You might also consider buying another drive (might be a good time to pick up an SSD) and installing it into the MacBook as a replacement.
Opening the MBPro and swapping out drives is a VERY easy task -- even I could do it.
One last thought:
About "urgently needing" files that weren't backed up...
... might be time to start thinking about a backup strategy.
I recommend either CarbonCopyCloner or SuperDuper.
If you had a CCC or SD cloned backup, it would be a matter of a couple of minutes to boot from your backup, get up-and-running again, and work on the problems from there...