I don't know if it's still the case, but ca. a year or two ago the computer magazines were worried about the need to have SD or other internal camera cards formated only by the camera, in the camera and there were warnings that formatting by the laptop might corrupt the memory on the card, and doesn't provide features that the camera needs in order to know how to talk to the card.

I never found a real explanation of what's different about the way the cameras format a card as compared to how the computer formats them.

Most digital cameras have a "format" entry somewhere on the menu, and if you can tolerate wiping the card, you might look for it and try formatting the card in the camera, using the camera menu. Once formatted by my cameras, I've never needed to reformat for the computer to read them, or when I put the card back in the camera.

I've only had a couple of cheap cameras, but never had to format a new SD card to get one to work in both camera and reader, although I have done an in-camera format since the user manuals say you should; but Vista did cease recognizing my latest camera (about 5 years old when it happened), and neither method of formatting recovered the ability to make the computer recognize the memory so I could download the photos via a USB cable, so I just use a reasonably decent reader, or plug the card into the SD slot on my new computer or on one of the printers.

USB needs to find a "device identity" on a device in order to mount it when you plug it in, and my guess is that OS version updates and patches probably omitted the "name" for my camera from the PNP libraries that came with the later OS versions. That may be a rational guess (SWAG) or just a hallucination, but I never found a cure for it.

An alternate "explanation" posited by one correspondent was that formatting in the computer may wipe out the PNP device identity code, making it unrecognizable and thus unmountable.

On better (>$$$$) cameras you may be able to download utilities to recover a corrupted camera menu, which might possibly be an unlikely part of your problem; but they don't provide anything of that sort for my cheap junkers.

John