@Mahesh: Today I turned on my computer (another than I used last time) and what do I see?! The sidebar-primary appears at the left side as it should be. I think there has to be a problem with the browser. I will check that later.
Now I have got the same problem like before. The space between left colum and content on the riht is to big and I can not find the setting. The default layout is set to primary sidebar, content. Could there be something in the php file I do not see with firebug?
Big thanks for helping again.