Images not Appearing

I am using Arras theme in a WordPress MU site and everything seems to work perfectly fine until yesterday. Images are not appearing as well as my header.

When I go to Media Tab in Dashboard, and copy paste the URL of an image into a browser, I would get an error:
Error 404 – Not Found

We’re very sorry, but that page doesn’t exist or has been moved.
Please make sure you have the right URL.

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If anyone knows the solution, I’d be glad to know. Here’s my site: https://www.ph.dotatalk.com