Do not open it. Ever.
Get a new drive and rebuild your system. Then, maybe connect that dead thing as a secondary and see what you can pull off it if anything.
If it's not recognized in the BIOS, either it is a bad cable, bad motherboard port, or a bad drive.
But the more you mess with a potentially bad drive, the smaller your chances of getting anything off of it.
The best choice is to simply buy a new drive, rebuild the system, and get your data from whatever backup you have.