The "open" and "save" dialogs are OS dialogs. Photoshop doesn't really control the dialog.
Did you hide the devices section in the left-hand panel of the open dialog? (there's a rollover button that says "show" or "hide")
Nope, all the other devices are showing (Hard disc, iDisc and Memory card). Any ideas how I might control the dialogs within Mac OS X?
Probably the hard drive is not powered up. Put your hand on it and see it you can feel it spinning. If not it is probably off. If it is spinning then try rebooting computer.
You may have accidentally dragged the drive out of the Devices list in the sidebar.
In a Finder window with visible sidebar, do Shift+Cmd+G to get the Go To Folder dialog. Enter
then click OK.
You'll see all your mounted volumes in the Finder window. Drag the required one to the Devices list in the sidebar.