Does your theme perform this important step?
Strong Testimonials, like many other plugins with front-end output, expects your theme to perform critical steps. Unfortunately, some themes do not.
Your theme must call wp_footer in order for the slideshow, pagination, and form validation to work.
In general, your theme should also call wp_head but Strong Testimonials does not require it.
To check your theme for important stuff like this, use the excellent Theme Check plugin.