500 Internal Server Error after installation

After I installed this plug in in my WP site http://www.assamsocietyqatar.org the admin dashboard and the site itself can not be viewed. I am getting error as below :-
“Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator to inform of the time the error occurred and of anything you might have done that may have caused the error.
More information about this error may be available in the server error log.”
Kindly help.

https://wordpress.org/plugins/nextgen-gallery/