My Nikon D50 worked fine for two years. This morning my PC doesn't recognize the camera. I recently took the memory card out and replaced it. The camera does take and store pictures fine. I tried a different USB cable that works fine with my external hard drive, so I don't think it's the cable. I tried the camera on another PC and a Mac, and they don't register the camera either. I have the settings set to "Mass storage" on USB port. Please help - I'm about ready to go on a trip and need to take pictures for my work.\r\nThanks!