How to link DLL in bindings.gyp for node addon on Windows 7

Question

I want to access DLL in my node addon. I configured my binding.gyp like this:

{
 "variables": {
  "dll_files": [
    "AUDIOPRO.DLL",
    "AUDIOSEA.DLL",
    "AUDIOSWA.DLL",
    ]
 },
 "targets": [
    {
        "target_name": "addon",
        "sources": [
            "Main.cpp"
        ],
        "libraries": [
        ]
    }
 ]
}

I tried like this in Main.cpp:

const char* processAddress = "../AUDIOPRO.DLL";
HMODULE processModule = LoadLibrary(processAddress);
if (processModule == NULL) {
  // always enters here
}

The problem is that processModule is always be NULL, I don't know why....