Thanks for your help so far guys, apologies for the delay. I have now seemed to fixed the thumbnail issue by regenerating the images, a simple issue!
I'm now on with the blank screens. I host the site on my own VPS so I have full control over all aspects of the software that runs on it.
I seemed to remember that when I installed the software, there was a cross next to "Disable magic quotes" but I restarted my server with both Magic Quotes installed and not installed and the cross never changed. I wonder if there's something else that I need to do?