Nikon d3000 not transferring photos to iphoto?

I have a nikon d3000 camera and i usually just plug it in to my mac and turn it on. It usually starts transferring the photos right away but i did the same thing a few minutes ago and it isn't working. I use a usb cable and that's all i have. Is there any way to make it transfer to my iphoto?

Try putting the SD card directly into the computer

that way, there's no middle device, which is yet another thing that could cause errors

If you absolutely need to do it via USB cable instead of card reader, try rebooting the computer. That will most likely fix the glitch.