Images and videos not readable from SD
This might be some compatibility issue -- despite the fact that it seemed to work fine initially.

It's not the first time I read such in connection with a class-10 card. I'd recommend to get yourself a class-6 (good enough and fast enough -- only in rare cases you would really note any difference), maybe preferably from a different brand than the current class-10, and give that a try.

Chances are very good your trouble will disappear this way.