R6400 - ready share access to HDD by MacBook Air stopped working

This has been resolved!  Not sure why but it is working.  I do know what I changed though. 

There was a printer plugged into the back USB port.  I removed the printer and plugged in the HDD.  After a few moments, the white light for the rear USB slot went on and the readyShare drive became visible in Finder on my MAC and all the data is there.  For the record I tried moving the drive back to the front USB slot and the light for the front USB port remained off and the drive did not show up on Finder.  

Is it possible for a USB slot to go "bad" out of the blue?

Regardless - the router is functioning well enough.  Thank you for the service call - it coincided with my getting the router to recognize the HDD but it was still appreciated.  The unit is way too old to be covered by a warranty but it is back to doing the job. 

Thanks again!