Uaooo, many thanks Denzel,
My images now are shown perfectly.
Although I continue with the problem of not being able to edit slides because I don´t have the box of featured image in Theme4Press Slider as you can see here: http://valledental.es/wp-content/uploads/2016/07/Theme4Press-slider.png
Do you think this problem will be solved in a future?
Thank you so much