I haven't seen Mount. Mine does give me the option of mass storage so I just press connect. Could your card be defective? Or maybe the connections dirty? Write protection will let you see what's there but nothing else, usually.
What happens if you try putting your card in a reader? Ativa among others has USB readers that will hold the mini SD with no adapter.
I'd try checking the card in a reader first. Cheapest way to start.

 

I can see my card with either method. I meant take the card out of the phone and use a reader.
I just had a screwup where an SD card for a camera decided it was write protected without my flipping the little switch thing that physically prevents overwriting the card.
Some software had stuck that write protect on there - You could have downloaded something that is disabling the read. If you can't read it using a separate reader, then the card is bad. The card would read/write/delete in the camera.
If you can see the card using Samsung software, then transfer everything off and format the card. Then transfer back and see if you can read it.
You can get the drivers from Samsung or maybe there is a link here.