winapi's LoadImage() alway returns NULL - c++

Question

I've tried to load a bmp image using LoadImage() in order to display it, but I just can't find a way to load the image. Here is some code:
EDIT
as suggested, here is a runnable example
#include <windows.h>
#include <iostream>
#include <fstream>
std::string GetLastErrorAsString()
{
//Get the error message, if any.
DWORD errorMessageID = ::GetLastError();
if (errorMessageID == 0)
return std::string(); //No error message has been recorded
LPSTR messageBuffer = nullptr;
size_t size = FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
NULL, errorMessageID, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPSTR)&messageBuffer, 0, NULL);
std::string message(messageBuffer, size);
//Free the buffer.
LocalFree(messageBuffer);
return message;
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpszArgument, int iShow) {
std::ofstream file("output.txt");
HBITMAP hBitmap = (HBITMAP)LoadImage(NULL, L"C:\\yes.bmp", IMAGE_BITMAP, 300, 300, LR_LOADFROMFILE);
if (hBitmap == NULL) {
file << "error: " << GetLastErrorAsString().c_str() << std::endl;
return 1;
}
else {
file << "success." << std::endl;
}
return 0;
}
And this result is always NULL. If I put a wrong file name, the error message will be The system cannot find the file specified. but if the name is right, there is simply no error message.
I've tried to save the bmp file in 24 and 32 bits, I played with the LR_ flags, it doesn't change anything.
I also tried setting the HINSTANCE to the main's one, without any success.
I run this code once at the beginning of the main.
Thanks for your help, I hope I just misunderstood how this works