Question: I have a Visual Studio 2010 solution with a few projects. I can successfully build with Build -> Build Solution or Build -> Build MyCompany.MyProduct.MyProject. After building I press CTRL+F5 and successfully run the start up project. This works as expected.

After I change a source file, save it and then again build (with either Build -> Build Solution or Build -> Build MyCompany.MyProduct.MyProject) it builds successfully. I am still able to press CTRL+F5 and run the startup project. This again works as expected.

The problem is in the following scenario:
After I change a source file, save it and directly press CTRL+F5 then Visual Studio 2010 says BUILD FAILED and there are no errors. And it doesn't start my startup project (of course).

Am I missing something?

Answer: 
I closed my visual studio. 

Deleted every bin folder. (I had a weird permission error, so I deleted the files and back track deleted the folders including bin). 

Reopened visual studio. Performed build or rebuild and everything was working again.
My issue arose from converting a functional vs2008 project to vs2010. All other projects in the solution came across fine, but this one would build the MIDL portion, then stop and fail. Detailed build setting revealed nothing, so finally I created a whole new project with all files the same. This worked. Then I compared the settings, and finally after changing the various parts to match, I discovered that the converted project had MIDL->General -> "MkTypeLib Compatible" set to blank. This was a valid setting in vs2008 apparently, but in vs2010, it apparently must be set to Yes or No (or inherit).

This has fixed my issue.