MacBook Pro doesn't recognize External Hard Drive

Here's what works for me:

1. Hold down "option" key and select "System Information" from the Apple logo in top left corner of screen.
2. In Left column of drop-down, scroll down to "USB" in device list
3. In right column, scroll down...the device you are trying to connect should be listed (if not listed, this solution will not help you)
4. Select the device, leave it highlighted, and minimize-Do Not Close- the dialogue box.
5. Go have a cuppa. When you come back, the device icon should be on the desktop.

Works every time for me (fingers crossed).