Why won't my laptop recognize my Nikon D40x?

I have my Nikon D40x connected to my computer with a camera cord in the USB port. For some reason, it will not show up in my finder window under the Devices, however. The camera is on, the battery is charged. I know it isn’t the camera or the cord because I tested it in my roommate’s laptop and it worked. I also tested my external hard drive in my port, and it was able to mount. Is there any way I can make my computer find this device so that I can retrieve photos? Another thing to note: when I turn off the camera or disconnect the cord, the computer still realizes that I am removing a device. I just can’t make it show up!