Dear Friend,
Please deactivate all 3rd party plugins in your website.
And make sure your all plugins and also theme is updated. we are running at theme version 3.8 and you are using 3.5. and some of your installed plugins are of version 3.8 supported. it might cause a conflict.
please make sure everything is updated. then let me know if the issue occur.
Refer this tutorial:
https://www.youtube.com/watch?v=2aEMLpLD4lc
Regarding the update in the Page Editor, it is because of the latest update of Wordpress.
I can only suggest you that you can install 3rd party plugin Classic Editor
Refer:
http://prntscr.com/ltekdv
Follow the steps:
https://www.youtube.com/watch?v=1Yme3TR-Km8
Best regards.