PC not reading 16gb SDHC card but works in camera


I have a 16gb Ultra SDHC card and i’ve taken pictures with it in my Canon G12 camera.  I can play back photos in the camera but when i plug the camera to PC via usb cable, the computer does not recognize the drive.  I’ve also tried using a usb card reader but it doesn’t work.  I swapped sdhc cards on both the camera and card reader and it works correctly.  Is there anyway for me to retrieve the photos in the 16gb card?

thanks for the help.