usb ports not reading...

I am trying to upload photos from my nikon and never had a problem before until now all of a sudden neither usb

port will read my camera's usb to upload pics to my iMac. Before some of them wouldn't always work

like with my (iPhone 5) but lately it works again so it makes me worry something is wrong somewhere else.

I tried resetting the pram (holding down command, option, P,R) keys that didn't help. Any suggestions to get the usb back?

Thanks in advance.