Page-Wrapper ends in middle of content

Hey everyone,

got a little problem right here.
I'm using the wp-blog module to generate blog posts at the front page.
To make it look better I styled the block around the wp-blog-posts with an bgcolor etc. etc.
The page-wrapper got the same css-styling but somehow it just ends in the middle of the wp-content, at the same end as the sidebar-block.
So somehow the wrapper doesn't see the blog-content and just ignores it.
How can I fix this?
I'm really sorry for my bad english, it's very hard to explain such complex issues but I hope you get the point! If there are any questions, please don't hesitate to contact me (alex.ruttkowski@gmail.com).
I also attached a screenshot for better understanding, you can see part of the slideshow, the highlight block (acting as a menue), the main content (blog posts) and the sidebar.
The blog-block and the sidebar-block got custom styles just as the page-wrapper.

Thank you very much!

The firebug-inspect function showed me the height is 970px