Files are apparently gone/ turned to symbols

I have a zoom h1. It has been fantastic. I have an important file. I plug it into the computer. All the file names turn to symbols. I try to open the one that I know is "stereo" where the files are. All files are symbols now. Then... I shut everything down and start back up. Now it says F:is not accessible. Location is not available. The volume does not contain a recognized file system. Please make sure that all required file system drivers are loaded and that the volume is not corrupted.