I don’t know what the problem is yet, but I see the sidebar and footer when viewing with Firefox. It’s not there with Internet Explorer. This tells me that something must be too large in size and is causing IE to misbehave.
ETA: Or maybe that’s not the problem. I would highly suggest that you validate your CSS and XHTML. There are a lot of errors and that alone could cause the layout to break.
I have installed many themes and plugin. I am not sure the causes? Should I deactivate the plugin or change the theme? Initially I have changed the theme many times and upload the plugin at the same time. Then the sidebars and footer suddenly dissapeared.