So I have a flash drive that I used before I got my mac on a pc. When I got my mac, I knew I would have to reformat it to be able to use it for both. I did so, but there is one problem. The flash drive works fine in windows, but won't even show up on my macbook. I insert it, open up disk utility and it isn't there. I have no idea what to do, does anyone have an idea?