overnighttolondon on "Updating to PHP5 = blank white admin"

Ok so a few things were a bit out of date on my site and server.

Updated PHP to 5.4.22
Blog still works fine user-side, but now my /wp-admin shows only the left column (right page area is blank)

Seemed like similar issue to this user:
http://wordpress.org/support/topic/white-blank-admin-for-php5?replies=3

Tried disabling all plugins by moving them to a "disabled plugins" folder, but no love.

I'm still on WordPress 3.3.1 which maybe isn't compatible with my PHP version?

Thoughts on the best approach here? Roll back PHP? Update WordPress without going via wp-admin? Using a custom theme that's old and might be a bit delicate to update with but I'm game to try it. I have a backup.

Thanks!