Always Recompile unnecessary files (not modified files) [SOLVED]

I'm having trouble with Visual Studio .NET 2003.
I was developing an application for one year ago and when I clicked to build solution, it compiles only the files that where modified.

Since one month ago I have reinstalled Windows and Visual Studio and when I try to build the project, it always compile all the files in the project.

I don't understand what's happening because I didn't changed any option.

Thanks,

-SOLUTION-

Hi, finally I have found the problem. I have a "definitions.h" file that contains some definitions. One of this was the PI number. Now I have deleted this definition and I use the M_PI constant from "math.h". I don't understand why but now the project only builds if I make any change and only compile these files.

[765 byte] By [NyAw] at [2007-12-30]