i can’t write new posts or edit the old ones,this problem is with page and post

when i try to edit or make new post or page,then the area where we write post is not working correctly.
1.)
I login to my dashboard
2.)
then i click on post , add new
3.)
when the page open i doesn’t show the cursor or old post , instead it shows a white blank page in the post area , while there is a post that i have already written working on my site, the only problem is in backend.

i know its very difficult to understand what i am saying but the problem is complicated to tell …..Basically the area where we write post or page is not working the way it should , it is not showing any previous post nor letting me write new posts.instead it just show blank page..but the post are live on my website ,so the only problem is in backend of wordpress. i hope you understand.

The page I need help with: [log in to see the link]