请教钩子方面的行家指点

ibrary HKTest;// WH_KEYBOARD Hook Demo
// 1. Project | Compile 编译连结成 HKTest.DLL
// 2. 开启 HookDemo.DPR
uses
   HOOKPROC in 'HOOKPROC.pas';exports
EnableHotKeyHook,
DisableHotKeyHook;begin
hNextHookProc := 0;
// 以下这两列, 旨在确定 DLL UnLoad 时, 确定将 HOOK 解除
   //To keep the exit chain intact,
   // you need to save the current contents of ExitProc before
   //changing it to the address of your own exit procedure
procSaveExit := ExitProc;
ExitProc := @HotKeyHookExit;
end.// in HOOKPROC.pas fileunit HOOKPROC;interfaceuses
Windows, Messages;var
hNextHookProc: HHook;
procSaveExit: Pointer;
function KeyboardHookHandler(iCode: Integer;
wParam: WPARAM;
lParam: LPARAM): LRESULT; stdcall; export;
function EnableHotKeyHook: BOOL; export;
function DisableHotKeyHook: BOOL; export;
procedure HotKeyHookExit; far;implementationfunction KeyboardHookHandler(iCode: Integer;
wParam: WPARAM;
lParam: LPARAM): LRESULT; stdcall; export;
const
_KeyPressMask = $80000000;
begin
Result := 0;
If iCode < 0 Then
begin
    Result := CallNextHookEx(hNextHookProc, iCode, wParam, lParam);
    Exit;
end;
// 侦测 Ctrl + N 组合键
   if ((lParam and _KeyPressMask) = 0) and   //(lparam and $80000000= 0) -->down   <>0 --> up;
     (GetKeyState(vk_control) <0) and (wParam = Ord('N')) then
begin
    Result := 1;
    keybd_event(65,0,0,0);
    keybd_event(65,0,KEYEVENTF_KEYUP,0);// 模拟输了字母A   end;
end;
function EnableHotKeyHook: BOOL; export;
begin
Result := False;
if hNextHookProc <> 0 then Exit;
// 挂上 WH_KEYBOARD 这型的 HOOK, 同时, 传回值必须保留下
   // 来, 免得 HOOK 呼叫链结断掉
   hNextHookProc := SetWindowsHookEx(WH_KEYBOARD,
KeyboardHookHandler,
HInstance,
0);
Result := hNextHookProc <> 0;
end;
function DisableHotKeyHook: BOOL; export;
begin
if hNextHookProc <> 0 then
begin
    UnhookWindowshookEx(hNextHookProc);   // 解除 Keyboard Hook
     hNextHookProc := 0;
    MessageBeep(0);
    MessageBeep(0);
end;
Result := hNextHookProc = 0;
end;
procedure HotKeyHookExit;
begin   if hNextHookProc <> 0 then DisableHotKeyHook; // 如果忘了解除 HOOK, 自动代理解除的动作ExitProc := procSaveExit;
end; end.//调用方式如下function EnableHotKeyHook: BOOL; external 'c:/HKTest.dll';function DisableHotKeyHook: BOOL; external 'c:/HKTest.dll';
procedure TForm1.Button1Click(Sender: TObject);
begin
EnableHOtkeyHook;
end;procedure TForm1.Button2Click(Sender: TObject);
begin
DisableHotKeyHook;
end;
里面的这两句keybd_event(65,0,0,0);
    keybd_event(65,0,KEYEVENTF_KEYUP,0);为何不起作用百思不得其解！！！！