Header image displaying twice & other problems

I’ve just returned to my website for today and have noticed that suddenly (and without changes from me) my header image is tiling despite this option not being selected in the options.

Also, the background for my menu below the header was white until today. Now the repeated header image is behind it.

Also, my articles page http://salsahackers.com/blog has some strange things going on with the header. The whole page body is wider and the header is tiled in both directions.

And finally, when I click on the menu option ‘buy dance shoes’, I am taken to one of my blog posts.

I repeat- I haven’t changed a single thing on the site.

Please can anyone help?

The blog I need help with is salsahackers.com.