It looks like you have some additional HTML on your page that is breaking the page layout.
You've included this large block to your header file:
If you look at the bottom of that block, you will find a new table gets created. Its the table with the defined class name of "main_content".
It begins and then never gets properly closed.
Now if we travel all the way to the bottom of your HTML, you are closing the page with the following code:
Right off the bat, I can see a quite obvious error:
I would suggest that you revert your additional code back to stock (make a backup of it), and try loading your page again. It should now present itself as you'd expect
Debug your custom stuff and if you choose, return it back to your page when fixed.