The operating system sends the DBT_DEVICEARRIVAL device message when a device has been inserted and becomes available.
To send the DBT_DEVICEARRIVAL device message, the operating system sends the WM_DEVICECHANGE message with wParam set to DBT_DEVICEARRIVAL and lParam set to the address of a DEV_BROADCAST_HDR structure identifying the device inserted.
dwData = (DWORD) lParam;
Return TRUE.