customize

I've been using simple one template for a while..and for a couple of weeks i'm experiencing some troubles when I want to customize it. It doesn't preview the theme on the previsualisation. I want to change my front page from a dynamic one with the latest posts to a static one...Moreover, when I manage to do it, the website is down for an hour.

the website is www.destiempourbano.com and the problems happen at http://www.destiempourbano.com/wp-admin/customize.php how could I solve it!?I'm desesperate!