Memory Card Has RAW Format

"My memory card has changed to RAW file system which was FAT32 before. I have used this memory card for a few years in my mobile phone. Yesterday, I plugged my mobile phone to my computer through a USB cable and saved some music to the memory card. When I was transferring the music, Windows system says please insert a disk into drive. Then, I unplugged the mobile phone and reconnected it to my computer again, this time the Windows recognized my memory card as a RAW drive and it prevents me from accessing any data on the card. I also tried to move the memory card out of my mobile phone and connect it to my PC via a card reader, but system still detected it as a RAW drive. Can anybody tell me what is wrong with my memory card and how to convert RAW to FAT32 with data back?"