Just for info I suppose as I can't show you the problem any more, but the latest release of "All in One Event Calendar" by Time.ly breaks the Graphene slider.
The space for the slider is there, but is completely blank. Disabling the calendar plugin brings back the slider.
Afraid I couldn't leave my site broken, so have rolled back to an older plugin version and it's all fixed for now.
If anyone has a development or test environment and wants to see then its the v1.90 Standard version of the plugin.
Seems to be a (relatively) widespread issue - there are mentions on the Wordpress support forum and a few on Time.ly Support too.