I think i found my issue, No idea how, or why, but here goes..

I selected an invisible object went along to the renderLayer node ticked the global box for 'Render Layer Options' and suddenly all my objects reappeared. I dont understand how i unticked this or even why this option would effect the viewport. All my layers including render layers were visible.

Maya seems glitchy and slow atm, may have to try rescue objects and start again anyway.

Thanks everyone for your help