My Mac Mini will not recognise my iPod Classic MB565

I am running iTunes 11.0.2 and I accept all updates. I cannot find the OS for the iPod but it has everything that I have been offered.

I haven't sync'd the iPod for aboput a month and today the MacMini will not recognise the iPod. It isn't showing in iTunes or Finder.

Does anyone have any ideas please?

Thanks,

Bob