MEMORY CARD ERROR WHEN LOADED

Hello there,
I have a Micro SD card of 8 GB. It has a lot of content which I had stored there. It was about 4 GB. But now it has started giving error messages saying the memory is full. In addition, most of the files are now having "a question mark" instead of the real file icon. When I tried to open it, it tells me that the format is not supported. I am doing all these on my phone. What should I do to avoid losing more data.
Are these problems repairable?
Thank you in advance.
