I've got an iMac and a apple notebook and for either one, it won't let me add or move files onto it. It can let me take files out of it though. What's weird is it used to be able to but this just happened a couple of days ago, when I go to drag files onto it, it comes up with a circle with a slash sign. Is there any way I can fix this problem without having to reboot my hard drive and erase everything? I might of just accidentally changed a setting but not that I know of.