i was going through the same problems. went through the above steps and got my Hard Drive to amazingly showed up, then miraculously vanished again yet showed up in disk utilities...
i think what is going on is that my hard drive has a sort of sleep function cause when my computer went to sleep then woke back up my hard drive mounted and is running fine... so maybe we just need the computer to go to sleep with the hd plugged in?
will keep u updated if i go back to invisible state.
I have the same problem too! the day before yesterday it would read it on my MAC, then i added some files onto the HD on my PC at work, now it doesnt show up.. I have a program installed on my MAC so it can read a Windows formatted HD. There is nothing wrong with the hard drive as when i plug it into my WD Live Media player it works & reads files perfectly. It just wont show up on the desktop to open HD and access files.
Does anyone know how to fix this?
My external HD iomega wasn't showing up either.
In the end, it showed up when I connected the 2 usb for the HD to the iMac USB ports, insted of going through my Kensington USB hub ..