activating Marketpress causes changes to Theme

When I activate marketpress on WP site using a WPShower theme called Sight, the theme changes drastically and a lot of things don't even appear on the page.
Does anybody have ideas about how to prevent Marketpress from hijacking the theme's design?
Any Help Appreciated,
Luke

This is a link to the website, though Marketpress is currently not activated:
http://www.bromptonuschampionship.com/bromptonracing/