thumbnails suddenly fail to display and are broken in dashboard and front page

HI
Please help!!

I have run a website with two language by the plugin Qtranslate. Everything is working fine, but all of the sudden, thumbnails fail to display both on the left hand side of dashboard and website’s front page.As for the front page, i have widget activated to display both text and flag for website, but fail. At the same time, the thumbnails in dashboard turn to grey without color and some got broken as well shown below:

https://i58.tinypic.com/2a9e05h.png

flag of language selected fail to display on website’s front page:
https://postimg.org/image/5nw78o36x/

normal display:
https://postimg.org/image/qanoebrdd/
https://postimg.org/image/4vzlkjhxb/
https://postimg.org/image/tgfo1yucz/

Please help