I appreciate all the comments and help with this. So after weeks of pretending this problem didn't exist (May was an effed up month), my boyfriend and I gave the hard drive another go.
1. Tried new caddy. No new results. The lights come on and it whirs, but doesn't show up in my computer except briefly when it's unplugged.
2. Ran chkdisk, which said that the device was fine.
3. Installed the hard drive as a slave in my tower. And whoohoo!! The fun began!!
We got a black screen that said, "Disk boot failure: System halted." My boyfriend worked on it from there, so I don't know what he did, but in the end, we had to remove the 250gb hd. Then my computer wouldn't work at all.
LOL!!!!! THE EXTERNAL HD ATE MY INTERNAL HD'S OS!!! HAHAHA.
So my boyfriend tried a few different things. He created a partition and installed a new OS, but couldn't access any of my files. Finally he ran a recovery program and got most of it back. So now my internal hd is almost full because not only do I have the recovered files, but it's storing the same files in their original, inaccessible state, so I can't even delete them.
My external hd is still not working. He's taking it back home with him, and at this point, I don't care. I never want to think about it again.
And here's kudos to Max Bloom, because the one good thing that came out of this is that I'm shooting film again and getting back into toy and homemade cameras. The bad thing is it will probably be another six months before I'll have enough material for a portfolio or another show. But I'm getting back on the horse.
Thanks again for everyone who offered advice on this.