I use Visual Studio 2010 to debug a asp.net MVC project in my local machine. The steps are:
Click Debug and try to attch process "w3wp.exe". However it is not in the list.
I am sure "Show processes in all sessions" is clicked.
w3wp.exe won't show in the running process' unless there is actually an instance of the web application running.
Try to access your web page first, when it is displayed for the first time, try to attach your debugger. The process should now show up.