As you are using KDE 4.8.3 you are few steps ahead of me; however...
It would be helpful to know how your External HD is formatted and connected.
Mine are usually ntfs. I'm still using KDE 4.6.5 but I recall needing ntfs-3G and ntfs-config from Synaptic;
and enabling Removable Media under Configure your Desktop (KDE) -Hardware - Removable Devices.
This has worked for as long as I can remember.