I have done a search and could find discussions on this and the only thing I have heard is updating the software on the Galaxy S4, or turning off the phone, remove battery, replace batery and restart...I have tried all of this and my problem persists.
The Micro SD card is a PNY micro SD HC 32 GB card and it worked just fine for several months since I bought the phone new. For a couple of weeks now the phone won't recognize the card, when I go to storage settings under the micro SD section it says "Mount SD card, insert SD card" when the card is installed.
Like I said, this has worked for months with no problems and I have not made any changes or have ever removed it before this happened. And yes I am sure my phone software is up to date. Some other discussions mentioned "remounting" the card... but no ever mentions HOW to do that! They said they had to do it after every reboot, which would be at least a step in the right direction and allow me to use the music stored on my card. Please help! Thanks in advance.