Iomega External Harddrive not found

Try a different port, different USB cable, and a different PC. If it only works on the MAC now, you may need to just get another one for the other computer.

Thank you, I did and still does not work. It must be defective.

You may be able to get the data from the drive, could be only the enclosure is bad. Take out the drive from it, and connect it directly to the computer.

If it's new, just replace it under warranty unless you need your data. Then tell them what is going on before you take apart the case or they won't replace it.