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have you done a search for blank page? There must be literally hundreds of posts in this forum and the FAQ dealing with blank page issues.
Turn on debug in your system admin -> preferences -> general settings page, and this will show what is causing the blank pages. Without information like that, your XOOPS version, the versions of the modules you have installed and what actions you have and are performing, it's rather difficult to determine the exact cause, and suggest a solution.
Herko