Error LNK 2005 & LNK1169 C++ Visual Studio DLL

I'm trying to create a DLL plugin for OBS, but when I try to compile a simple script it gives me the following errors -

Error   1   error LNK2005: _DllMain@12 already defined in dllmain.obj   c:\Users\user\documents\visual studio 2013\Projects\name\nameEnhanced\nameEnhanced.obj  nameEnhanced

and

Error   2   error LNK1169: one or more multiply defined symbols found   c:\users\user\documents\visual studio 2013\Projects\name\Debug\nameEnhanced.dll 1   1   nameEnhanced

I've created a simple script, which only has 2 files namely -

handle.h
nameEnhanced.cpp

these are my files -

handle.h

#include <windows.h>
#include <string>
using namespace std;

namespace MsgeBox
{
    class myMessage
    {
    public:
        static void createMessage(HWND windowsOwner, LPCWSTR theMessage, LPCWSTR theTitle, UINT theIcon){
            MessageBox(windowsOwner, theMessage, theTitle, theIcon);
        }
    };
}

and

nameEnhanced.cpp

 // nameEnhanced.cpp : Defines the exported functions for the DLL application.
    //

#include "stdafx.h"
#include <Windows.h>
#include "handle.h"

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
    MsgeBox::myMessage::createMessage(NULL, (LPCWSTR)"Hello", (LPCWSTR)"I See You.", MB_ICONWARNING | MB_CANCELTRYCONTINUE);
    switch (fdwReason)
    {
    case DLL_PROCESS_ATTACH:
        // attach to process
        // return FALSE to fail DLL load
        break;

    case DLL_PROCESS_DETACH:
        // detach from process
        break;

    case DLL_THREAD_ATTACH:
        // attach to thread
        break;

    case DLL_THREAD_DETACH:
        // detach from thread
        break;
    }
    return TRUE; // successful
}

I've tried to delete the dllmain.obj file but that didn't work

I've used https://msdn.microsoft.com/en-us/library/windows/desktop/ms645505(v=vs.85).aspx as a base for my code

I believe Visual Studio provides a dllmain.cpp source file with the DLL project template and you say:

I've tried to delete the dllmain.obj file but that didn't work

However that won't stop it being recreated every build. You need to clean the project and then delete dllmain.cpp from the project.