themes do not work


Now I tried to install all the themes of WPMU and BuddyPress and none of them appear after I click activate, all I have is a white screen and I am unable to access the dashboard, I have two different installations with WPMU and neither works. I made the installation of both mother and child folders of various themes and activated only child and does not work. How does not have to keep deleting the themes by FTP to get back to access.
I have already installed several themes in Wordpress and have never had this problem even tried installing a random theme in WPMU and it worked, only the themes that I download the WPMU DEV does not work.

Please help me.

Now appreciate the attention