WARNING This will format and delete all the data on the hard drive. It basically resets the hard drive for use on windows. So if you don't care for data, go ahead.
Try
- right clicking on the volume of the external HD (the part with the blue bar on it)
- select 'delete volume', which will turn it from blue to black and it will be labelled 'Unallocated'
- If you have multiple volumes, do this for each one, they will then combine into one volume afterwards
- then right click on the volume again and select 'New Simple Volume', click through that setup, don't bother changing anything, and that may fix it (it did for me).
From what I can tell, the hard drive isn't set up to work with windows for whatever reason, which is why when you right click on it, all the options are greyed out. It needs to be wiped and reset for use on windows. My hard drive ended up like this after using it as a TV recorder. So maybe it happens when used for non windows devices.