After certin edit to my admin panel i get white(blank) page

Aloha, when i edit users, delete plugins, make category and post edits it load back to a blank page from the http referer pages…

I have deleted all unused plugins
change php to no memory cap
checked my dbase it has no errors and no error in wp_options
deleted all files from my themes cache folder
and checked for odd .htaccess files
killed my feedsmith plugin and wp_e-commerce plugins
attempted suicide but could not

I am just a few days from launch and totally freaking out…
Please help it all worked until I added lightbox2 but it does the same with out without it.