lease try changing the following settings on your camera.
Change the camera's USB Connect Settings: Go to [MENU] - [ Settings] - [ Main Settings] - [USB Connect Setting] - [Mass Storage]
If the step above does not resolve the issue, change the camera's LUN Setting: Go to [MENU] - [ Settings] - [ Main Settings] - [LUN Setting] - [Single]
If that does work then replace usb cable
Try connecting usb cable to a 2.0 port
jim