Not too sure but you can try this as a troubleshooting step. Turn your phone off and take your memory card out> insert it to a memory card reader and save all the files in the microsd card to you computer (either with a program/copy & paste). After you have done this format your microsd card by going to My Computer> Right click on the microsd drive (e.g. g: )> Format>make sure it's FAT32/Default allocation/Quick format is unticked anf click start.

After all this again go to My Computer> Right click on the microsd drive (e.g. g: )>Properties>Tools Tab>Error checking press Check now> Tick Auto. fix file system errors and scan for and attampt recovery of bad sectors.

After all this copy your files back to you microsd card and reinsert it back to your phone, power on your phone and test it. If this doesnt work we'll have to wait for someone who knows how to fix this. Hope this works though good luck