Global Hook KeyBoadr in TService

Question

I want to write Global Hook. As an application, the code below works. But not as a service.

function TrapKeyboardInput(nCode: integer; wp: wParam; lp: lParam): LResult; stdcall;
// Windows Hook Procedure To Intercept Keyboard Input
begin
    // This Structure is Defined By The Windows API
    if nCode < 0 then
        Result := CallNextHookEx(hook_Keyboard, nCode, wp, lp)
    else
    begin
        if nCode = HC_ACTION then
        begin
            SecondInactionHO := 0;
            Result := 0;
        end
        else
            Result := 0;
    end;
end;

procedure StartHock();
begin
    hook_Keyboard := SetWindowsHookEx(WH_KEYBOARD_LL, @TrapKeyboardInput, HInstance, 0);
end;