My plasma screen will work fine a couple of hours and then the screen will go all 'jumpy'. I thought this was an overheating problem (which it could still be) but the problem sometimes dissapears after a while, most of the time you have to turn it off and wait an hour or so though.
The same hapend to me and I open the back cover and take a look serching for anything out of nature see nothing just unplug and re-plug di conection ribons and the problem was solve good luck...