I'm using Tererik:RadEditor in asp.net. When I click ImageManger it is shown totally broken. I have not applied any CSS to the page or any control.
How to resolve this issue?
This happens exactly because you didn't apply Telerik Css file to your control. To fix this, you need to add css file for editor control to your page. you can do it in markup or design mode by selecting skin.
If you're going to inspect your code, you should see 404 errors. Do you see them?