USB only recognizes Iphone, no other items.

So, over the last few months my USB ports have slowly stopped recognizing devices. My back up hard drive and my ScanDisk card reader. When I plug in my external hard drive, I can feel the drive running, the light comes on, but nothing else happens. I have tried restaring my computer, I have tried connecting and reconnecting...I even tried the Option+Command+P+R at start up. I don't know what else to do. The ONLY thing that works in either of the USB ports is my Iphone 4S. Not one issue at all with that. Any advise out there for me? Thanks in advance.