Blank pages through whole website

I am trying to finish my website with the plug in Qtranslate but since I installed it, every page is blank, the sidebar works as it should be but not the main page.

I tried to disable all plugins, it did not help.
I tried another theme, it worked but I could not find out what was wrong with the Theme I use which is Expositio.

Any help would be greatly appreciated, as i am totally new to this and don’t know where to look for the problem.