welcome to CTH, counselor
I'd strongly suspect hard drive total failure.
Two ways of checking what is going on here:
1) Try putting that suspect drive in a pc as a slave drive (for the purpose of this test, you could even try it in place of your cd/dvd drive
2) Try a known working drive in the external enclosure.
When you know what is going on, you can make a decision on your next step from here.