Question details toolbar not woking. its not show in Question details text area. and can't type some question details

this is my web site ask Question page http://developers.prathimana.com/?page_id=135
look this image http://prntscr.com/3pys76

Firstly, please deactivate all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one and let us know if you find the problematic plugin(s). Maybe there is a conflict in plugins.
If you still face there issue, you can send me username & password of your site for further checking (via private answer).

Its work! ^_^ Thank you.. conflict plugin is “WordPress Facebook” http://web-dorado.com/products/wordpress-facebook.html
I removed this plugin. now http://prntscr.com/3q4lk6