Have you looked on the Iomega website to see if there is anything in the support pages for you model that might help?
You could also post a query to their support team to see if they can add anything.
If you haven't already done so try with a different PC as well.
Apart from those you have exhausted my knowledge.
If you let me know the model of your drive I can check on a private support site I have access to.
The iomega site has
this article which includes the following:
Do not...
1. Connect or disconnect any USB device while any USB drive is transferring information. Data loss will result!
2. Use any USB cable with your drive other than the cable that came with the drive.
3. Use USB extension cables with your drive. Data loss might result.
4. Disconnect your drive or unplug power to the drive when transferring information.
5. Connect more than two drives with USB connections to a single computer.