Page Goes Blank!!

Hello!!

Basically I have a full website (php based).  I'm trying to define my edit areas so our client can go in and make changes.  However, when I select the page from the drop-down on the top left, it hangs and then a blank page loads?

It was working fine a few days ago, but now all of a sudden its loading blank.  I have tried rebooting, using another browser and removing all cache and history etc but still no luck :(

Love the software - SimpleCMS rocks!!

Help!!!!