Theme doesn´t work anymore

Hello, My web stopped working yesterday. It didn´t load at all. The only way to make it work was to change the theme, therefore it seems to be a problem with Catch Responsive. I would like to have that theme back, but it has basically disappear from my "installed themes" and when I try to install it again, it says that it is installed already. Could you please help me with that? Many thanks in advance