Here's what I'd suggest:
Sometimes DiskWarrior can repair a drive situation like this. Worth a try, but don't get your hopes up.
1. Download DataRescue (free to download and use in demo mode).
2. You will need a SECOND drive of sufficient capacity to serve as the "scratch and recovery" drive. You MUST buy or use a second drive. No way around this.
3. Launch DataRescue and "aim it" at the problem drive. Does it see it (even if it isn't mounted on the desktop)? If so, try the deep scan mode and see if it can recover anything to the scratch drive.
However, if the above doesn't work, you may need to go further:
4. Re-initialize the problem drive. YES, you ARE reading that correctly. Just do a "quick erase" but do not -- REPEAT, DO NOT -- choose to "zero out" the data by choosing "secure" erase. YOU DO NOT WANT TO DO THIS.
You only want a quick initialization so that the data "out on the sectors of the drive" will be left intact -- and RECOVERABLE.
5. Now "aim" DataRescue at the re-initialized drive and tell it to do a "deep scan". THIS MAY TAKE SOME TIME.
6. DataRescue will scavenge the sectors of the drive, and will re-assemble what it finds.
7. DR will let you recover ONE (and ONLY one) file in demo mode.
8. If this is successful, and if you can see a long list of potentially recoverable files, NOW it's time to pay the registration fee and get a code. Then you enter the code in DR and it does its thing, recovering the files and copying them to the scratch drive.
9. Be aware that you are going to lose previous folder hierarchies and many if not all file names. But this "is the cost" of data recovery. Your consolation is that you get the -data- itself back.
This worked for me on a "bad partition" that wouldn't mount no matter what else I tried.
No promises that it will work for you.
Be aware that professional data recovery on a 1tb drive is going to be VERY expensive. Probably over $1,000.