Frozen HTML tab and white visual editor text

Hi

I’ve set up WP multisite, created 3 sub-sites and was getting on nicely, but today I’ve hit a new issue with editing posts/pages which I’ve yet to resolve. I have added some plugins today, but nothing I haven’t used previously on other wordpress sites.

The problem occurs whilst editing posts & pages. The text (html) tab is not responding at all (ie. it’s there, but clicking it does nothing). The visual editor tab is working but the editor shows only white text.

I’ve tested in chrome, safari and a new install of firefox, all showing the same symptoms.

Here’s what I’ve tried so far:
– Cleared browser
– Set the theme to Twenty Eleven
– Disabled all plugins
– Added ‘define(‘SCRIPT_DEBUG’, true);’ to wp-config
– Added ‘define(‘CONCATENATE_SCRIPTS’, false );’ to wp-config

None of these have had any affect.

Has anyone else noticed this? Are there any obvious fixes to this that I’ve overlooked?

Thanks

Luke