USB Ports Not Recognizing your USB Devices?
The reason is unknown, however it can easily be resolved by restarting your MacBook. If the issue happens much too often, you can try the following:
Resetting the SMC – A macbook with a battery you can’t remove by yourself. (Built-in battery)
Step 01. Shut down your MacBook.
Step 02. Connect the MagSafe power adapter into your MacBook. If it’s already connected, leave as is.
Step 03. Press Shift + Control + Option + Power keys at the same time.
Step 04. Release all the keys from the keyboard.
Step 05. Press the power button to start your MacBook.
SOURCE: http://www.pntbrother.com/macbook-pro-usb-ports-not-working-reading-solution/