简单的MFC小程序在xp上可以, 在win7上不行,请教各位高手

class CMyApp : public CWinApp
{
public:
    virtual BOOL InitInstance ();
};

class CMainWindow : public CWnd
{

public:
    CMainWindow ();

protected:     
    afx_msg void OnLButtonDown (UINT nFlags, CPoint point);   

    DECLARE_MESSAGE_MAP ()
};

#include <afxwin.h>
#include "TicTac.h"

CMyApp myApp;

/////////////////////////////////////////////////////////////////////////
// CMyApp member functions

BOOL CMyApp::InitInstance ()
{
    m_pMainWnd = new CMainWindow;
    m_pMainWnd->ShowWindow (m_nCmdShow);
    m_pMainWnd->UpdateWindow ();
    return TRUE;
}

/////////////////////////////////////////////////////////////////////////
// CMainWindow message map and member functions

BEGIN_MESSAGE_MAP (CMainWindow, CWnd)
    ON_WM_LBUTTONDOWN ()  
END_MESSAGE_MAP ()


CMainWindow::CMainWindow ()
{
    //
    // Register a WNDCLASS.
    //
    CString strWndClass = AfxRegisterWndClass (
        CS_DBLCLKS,                                        // Class style
        AfxGetApp ()->LoadStandardCursor (IDC_ARROW),   // Class cursor
        (HBRUSH) (COLOR_3DFACE + 1),                    // Background brush
        AfxGetApp ()->LoadStandardIcon (IDI_WINLOGO)    // Class icon
    );

    //
    // Create a window.
    //
    CreateEx (0, strWndClass, _T ("Tic-Tac-Toe"),
        WS_OVERLAPPED | WS_SYSMENU | WS_CAPTION | WS_MINIMIZEBOX,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL);
   
}


void CMainWindow::OnLButtonDown (UINT nFlags, CPoint point)
{   
    CClientDC dc (this);
    dc.MoveTo(0, 0);   
    dc.LineTo(100, 100);
}