Estoy usando masm32 para compilar y vincular en Windows 7, lo cual funciona bien con el siguiente código. Sin embargo, invocar stdOut no es simplemente imprimir nada en mi línea de comandos. ¿Qué estoy haciendo mal?

.386

.model flat, stdcall
    option casemap:none

    include C:\masm32\include\windows.inc
    include C:\masm32\include\kernel32.inc
    include C:\masm32\include\user32.inc
    include C:\masm32\include\masm32.inc

    includelib C:\masm32\lib\kernel32.lib
    includelib C:\masm32\lib\user32.lib
    includelib C:\masm32\lib\masm32.lib

.data    
    MsgBoxCaption   db "Message Box Caption", 0
    MsgBoxText      db "Win32 Assembly is great!", 0

.data? 
    ; declare an uninitialized byte, referred to as location sum
    sum             dd ?

.code
    start:    
        mov eax, 1d
        mov ebx, 1d

        ; result will be stored in the first argument
        add eax, ebx  

        ; push eax onto the stack
        push eax

        ; pop value into sum
        pop sum

        ; invoke MessageBox, NULL, addr MsgBoxText, addr MsgBoxCaption, MB_OK

        invoke StdOut, addr MsgBoxCaption
        invoke StdOut, addr sum

        ; exit with status code 0 
        invoke ExitProcess, 0
    end start