Why is this happening to my phone's MP3 memory card?

To add and delete music from my memory card was fine but about a month ago I am no longer able to add nor delete any of the music on my memory card. Can someone please tell me why this is happening. Before I moved I had high speed and was able to add and delete music fine. Then I moved and had to use dial up but still it was fine. But a month ago we just got high speed again and I think from the time we got it my memory card has been messed up. I know that sounds weird but that's what happened.