The images could be a permissions problem, oryou might be running out of server space?
If neither of those, deactivate all plugins and see I'd the issue still occurs. If it's fixed, reactivate them one by one to find the culprit.
If it's still broken, switch to the twentyfifteen theme and see if that resolves it. If it does, then the problem is you theme.
If none of that helps, try manually reinstalling all the Wordpress files with fresh copies.
Whatever you do remember to backup first!