External drive troubles
 

Rather I think its the actually SATA drive its self, since the external case keeps power in good fashion.

The "symptoms" are normal spin up then click.. off.. spin up.. .. click.. off... spinup...... ... ... ... click.. OFF. Then it just stays there.

Brand and model:
WD2500 Caviar SE16.

Is there something I'm missing or is this drive truly toast.

I just had a Ex-case where, it would power up but the drive itself wasn't getting any of the power. I had to use the case for power for the USB connection and a system power connection for power to the drive.

I would test the power connections in the external case
Know where you stand with what is working and not..

And maybe think about a new HDD- the click of death never bodes well :(

Your observer is very good..

I did take the case apart and remove the power, etc.. to plug directly into another drive, when I tried to mirror a SATA to IDE.. ya.. it didn't work.

And it almost killed the drive, or maybe it really just killed the case, adapter..
Just get a new case, I'm savvy to that.