imac fusion partion problems

My IMAC harddrive somehow renamed itself '''''''''''''''...'''''''' instead of Macintosh HD. I can still use the drive but the ''''''' seems to be indication a corruption of some kind. I cannot rename it, I've tried mounting and unmounting it (doesn't seem to recognize it) so I can't reformat or reinstall the OS - but I can still use the IMAC and with finder get to all the files - any ideas?