Re : Some pages always blank in all versions
Pretty strange.
post_max_size only affects maximum size of uploaded content so it doesn't matter (8
MB is well enough).
Do you get this on any page when logged in as admin?
Does the page end the same way as Vacilando?
I thought that phpinfo would show memory_limit...?
At least your PHP version must not be the problem.
What about trying to disable as much stuff as possible?