sounds like your DVD HDMI video output is progressive vs your TV can only accept interlace. When a DVD player uses HDMI, it sounds like is a upscalling model. So, there is a possibility you upscale your DVD video out where your TV are not capable. So the possibility are:
1. Your TV is HD ready, which is 720P and you push your DVD upscale to 1080p or 1080I. ( or more than 720p)

2. Your TV can only support 1080I or your upscalled to 1080P.

Test it... I'm just guessing. So not sure whats your DVD player or TV models.

This post has been edited by tracktion3: Nov 15 2009, 07:49 AM

Not sure what DVD player you use. But some of them got a short cut button. My older Samsung DVD with upscalling capability will rotate the setting every time your press the button at the remote. It might be the case you accidentally or some one accidentally press the button. Have you check?

If you say all this while you run 1080i, then your TV cant support progressive. There is a high chance an accidental changes in your DVD player upscalling. Anyway, if I'm right, you might have tested it already.

So could be other cause.