I'm sorry if this is the wrong area to be posting for this but this forum is unfamiliar territory for me. My external hard drive has been corrupted and the error message is telling me to reformat it. However, through all the research I have done to find out how, everything I've found has told me to use Disk Utility to just erase everything on the disk to do this. When I try to do this, it tells me that I can't erase anything because the disk cannot be unnmounted. What should I do?