My computer won't detect my Nikon D5000! This has never happened before?

Okay so I went home today to upload some pictures on my Nikon D5000 to my Macbook. So I plugged in my usb cord and my Nikon responded but my computer didn't? I'm so confused this has never happened before. Every time I plug my Nikon into my computer iPhoto pops up and it immediately starts importing… Now nothing is happening… Help

Why aren't you just putting the memory card into the card reader on your computer? Usually files transfer much faster using a card reader and you will not be using up any battery power on your camera. Those of us who have been shooting digital images for nearly a decade, stopped using camera to computer cords about a few months after buying our cameras.

If you computer is too old to have a card reader, you can buy a USB 2.0 card reader for under $10

What usually happens when a computer will not "auto-play", it is due to a system update that prevents automatic recognition of devices as a security feature.

If you really, really want to use that cord, you can go into your computer and turn the "auto-play" mode back on, but I would not recommend it for security reasons and besides, card readers are much faster