How to debug into dll source file from web project

Question

I have web project and window project.Web project reference from window project and I want to debug from web project to source code in window project. Where do I setup to look for debug source code in window project.
I copied all source code from another computer. but on another computer can debug just fine.All that different is where the source file is located. so I think it should have some config in studio that tell where the source file is.

Edit : OK just reference dll in debug folder