Hey there, fbjunks.
I'm truly sorry to hear about the problems you're experiencing with your HDD. Do you have any data on that drive which you haven't backed up and you need to recover? Can you hear any strange sounds/noises coming form the HDD when you connect it?
You did pretty well with the troubleshooting so far. I'd also recommend that you try the drive with a different USB cables (preferably shorter than 12"), to see if anything changes.
If you don't have any data which you need to recover, you could download DLG (Data Lifeguard) and run both tests (Quick and Extended), to see what's the situation with the HDD. Here's how to do it: http://products.wdc.com/support/kb.ashx?id=NdhRFe.
Hope that helps. Please let me know how it goes.