If you are allowing Windows to use the HDN card as its "Default Playback Device"(in sound settings), I would change that so Windows uses the on-board sound card(Realtek?). That would leave the HDN card for ONLY Pro Tools(its worth a try anyway). Traditionally, Windows systems are best off when the PT interface is NOT used for Windows audio. If this solves the issue, there are many other ways to get non-Pro Tools audio to come out of your main speakers
