Don’t know if your blank page situtation matches this, but…
If blank pages are resulting just by modifying a theme, then restoring the original theme’s files seems like the first thing to try. I got my first blank page error yesterday, from making a typo when editing sidebar.php.
Simply undoing the typo did not make the problem go away, nor did unselecting and reselecting the theme. But when I copied the set of original theme files back to my wordpress folder, the theme started working again. The files which I restored (all of which had been modified at some point) were sidebar.php, style.css and header.php.
And yes, my theme mods all needed to be recoded. From now on, I will save my edits in sequential versions, and try to do sequential restoration of files as well.
Oh, I get it. You insert the more tag where the post is supposed to break.
I got the answer to posting with more tags over here:
http://codex.wordpress.org/Answers-Layout
