Theme woes

I've recently installed elgg, and thought I was getting to grips with it but I've hit a snag. I've tried to find an alternative to the default theme, and I've installed a couple in turn, putting the theme folder in the mod dirctory, enabling the plugin in tools administration and making sure it comes at the end of the list. The themes I tried did not behave as I expected, so I disabled and then deleted the folder. My expectation was that this would return the site to its default, but what I've got is a layout which is completely screwed.

Can someone give some pointers on what I might have done wrong and how to go about putting it right please?

(My site is