CRT looses synch when watching DVDs

[Muse]

I don't understand why it does this sometimes occasionally and sometimes it goes an hour or more without doing it. My Nanao F2-17ex 17" CRT monitor loses synch and acts like it's not connected to a video signal. All while playing a DVD movie. Is it because there's a moment of no signal, maybe where one scene changes to another? Is there anything I can do to stop this? If I move my mouse, it regains synch, but if I don't it remains black although there is a video signal. My system is Rigzilla in my sig. Thanks for any help.