Storage vendors don't want you to know this trick, but it can save you lots of money.
How to Use an External Drive for Internal Storage : Read more
How to Use an External Drive for Internal Storage : Read more
... or simply cut the (orange) 3.3V cable to the SATA power connector.
Too bad if you have one of those color-blind PSUs with all black cables...
If i understand you correct the drive and partition is visible, but it has no default drive letter assigned. Correct?... I see the drive in disk utility and it shows the partitions but I cannot mount/change drive letters. I need to get data off this harddrive.