Try sorting out the 73 markup errors. You have some serious errors in there due to missing closing tags. Then, if necessary, move onto the CSS errors.
http://codex.wordpress.org/Validating_a_Website
I checked this problem as best I could (this is new for me) and the vast majority of them appear to be associated with one plugin (I have contacted the plugin’s support).
It will be complicated and time consuming to delete this plugin (it is a recipe plugin and I own a food blog). Do you think there’s another option – something I can do?
In the page markup, there is one more “<div” than “</div” and they should balance. The missing closing div should go between the robin image and the Tags heading. For a quick fix, can you insert a text widget here that supports html. The only html present in this widget should be:
</div>
You will need to remove this when the plugin is updated.