I am following the HandmadeHero series. So far I have just finised a couple of lessons. When I run devenv and press F11 it starts the debugger but as I step over I am able to get a screen however that screen that is unresponsive with the mouse pointer turning to a blue circle the moment I hover onto the screen. But if I start without debugging, I am able to get a responsive screen. Here is the code segment

int CALLBACK WinMain(HINSTANCE Instance,
                     HINSTANCE PrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow) {
  WNDCLASSA WindowClass   = {};
  WindowClass.style       = CS_OWNDC | CS_HREDRAW | CS_VREDRAW;
  WindowClass.lpfnWndProc = Win32MainWindowCallback;
  WindowClass.hInstance   = Instance;
  // WindowClass.hIcon;
  WindowClass.lpszClassName = "HandMadeHeroWindowClass";

  if (RegisterClass(&WindowClass)) {
    HWND WindowHandle = CreateWindowEx(0,
                                       WindowClass.lpszClassName,
                                       "HandMade Hero",
                                       WS_OVERLAPPEDWINDOW | WS_VISIBLE,
                                       CW_USEDEFAULT,
                                       CW_USEDEFAULT,
                                       CW_USEDEFAULT,
                                       CW_USEDEFAULT,
                                       0,
                                       0,
                                       Instance,
                                       0);

    if (WindowHandle) {
      Running = true;
      while (Running) {
        MSG  Message;
        BOOL MessageResult = GetMessage(&Message, 0, 0, 0);
        if (MessageResult > 0) {
          TranslateMessage(&Message);
          DispatchMessage(&Message);
        } else {
          break;
        }
      }
    } else {
      // TODO(kskr) :
    }

  } else {
    // TODO(kskr): Logging
  }
  return (0);
}

The spinning blue cursor is probably due to the fact that you did not set a cursor in the window class.

WindowClass.hCursor = LoadCursorA(0, IDC_ARROW);