Thanks for this. I have tried all of these earlier in the day and nothing worked.
Weirdly it decided it wanted to work a few hours ago. Didn't do anything different just turned it on!
From what I can see looking around the forums it appears to be a issue with Mountian Lion and one I hope Apple decide to resolve very soon... Doubtful, but I can only hope!
In the meantime I've change the hibernate setting to 0