I have my PC connect to a 26PF7321/12 .
I switched screen resolution to 1920p in Windows 7 and all worked fine, also the picture was very clear even though the TV doesn't support 1920p.
After about 5min the screen turned black. I switched it off and on but it stays black, not even the menu pops up any more if I push the menu-button, but the sound is still there. The only thing to be seen is the litte Information in the top left corner which shows the Number+Name of the actual channel. But it disappears after 3 seconds.

Any Idea how to get the screen back to work.

I was thinking about resetting the TV-Software. Is there a way to do that?