It sounds like your hard drive might be having a problem with the hard drive itself. If this is one of those portable drives, then it shouldn't have been that much of a problem. But if it is one of the bigger desktop drives, you could have done some damage... especially if the drive was on.
It sounds like the USB backplane is still working and you could replace it with another hard drive, but if you're still under warranty, might as well work with their tech support. It's cheaper than buying a whole new hard drive. Since it was dropped, I'd be careful what you say if you do decide to talk to tech support.
If you use chat for Iomega hard drives they don't charge you for the call, so that's a plus. Here's a link to their chat line for tech support: https://iomega-na-en.custhelp.com/cgi-bin/iomega_na_en.cfg/php/enduser/contact_confirmwarranty.php