Secondly, you need to try a memory card recovery freeware to retrieve your inaccessible data. Actually, I also went through this write protected and unformatted memory card problem lash time. It had hundreds of my pictures and videos that I didn’t want to lose. Therefore, I tried many recovery tools on different webs. Fortunately, this freeware finally recovered the largest amount of my data unlike others. It was worth trying.
If you are interested in it, you could download it there: http://blog4mark.blogspot.com/2013/01/unformat-memory-c...
Thirdly, you need to format this card and assign a different letter to it for activating it again.
I hope my suggestions could help you.