There are two modes that Visual Web Developer and Visual Studio have: Edit mode and Run mode.  Edit mode is active when you are not running the web site and you are editing the code, or any of the files contained within your web site.  Run mode is active when you click the play button and bring up your web browser.  When Visual Web Developer is in Run mode, some of the functionality in the IDE is not available and either becomes hidden or disabled.  An example of this is the Toolbox window which gets hidden when you are running the project.  This is by design.  The designers of Visual Web Developer do not want you editing the project while it is being unit tested.  While technically you can edit some of the files as the program is being run, just remember that some of the functionality of the IDE will be disabled until you get out of Run mode.  To end Run mode and go back into Edit mode, all you have to do is close your web browser.  Once back in Edit mode, all the windows and other functionality should be available again.  Click here to watch a sample video where I start the web application into Run mode and then close my web browser to go back into Edit mode.