Search box invisble but not gone?

There’s no search box on your site but you need to reset the padding-right on #branding .only-search + #access div to zero in the theme’s stylesheet. But don’t edit the Twenty Eleven theme. It is the default WordPress 3.2 theme and having access to an unedited version of the theme is vital when dealing with a range of site issues.

Create a child theme for your customisations. Once your child theme is active, we should be able to help with the customisation.