It was working fine yesterday, I changed my desktop background, and today, all of a sudden, external disks do not show up on the desktop, even though I have it selected in finder preferences, I see it in the side bar, but not desktop. The main internal drive shows up but not my Seagate portable external. I tried going in and deleting preference files in the library and restarting, this did not work. The drive shows in the finder sidebar fine, but not desktop, also, firewire connected drives show up fine on the desktop. and I also tried plugging in a usb thumb drive, it showed, so it seems I have isolated the problem to the Seagate hard drive I am running mavericks 10.9.5. on a mid 2010 classic mac pro.