Question : visual studio 2010 not automatically rebuild

I'm using Visual studio 2010 professional. I'm working in a solution, but the visual studio does not automatically rebuild the solution after I press Ctrl F5, it ran the old version code. I have to rebuild the project manually. Especially, other solutions is working normally in visual studio.
What happend?
Thanks for any help.

Answer : visual studio 2010 not automatically rebuild

One of the cause for ur problem is that when you click on built your project is not build.
Right click on the root solution and select Configuration Manager.
In that check the project project for build.
Please confirm is this build check or not.