External HD has suddenly stopped being recognised.

We more or less filled our 1tb internal HD and opted to buy a 5tb external to give us some more capacity.

Plugged it in, formatted it. All working fine, great, started moving some stuff over.

This afternoon I decided to play a little and discovered I couldn't access some of my games. I have now figured out that for some reason the PS4 has completely stopped recognising the drive. It just says that there are no USB devices connected.

I have turned off the HD, then the console, then both, then the console first. Tried both USB ports, checked the cable is OK, sacrificed a rubber chicken... You get the Idea.

I have driven myself crazy trying to Google the problem, all of the articles I can find are about new HDs that people have forgotten to format.

Can anyone shed some light before I snap and break something.

Thank you in advance!