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Ok, I understand. Go ahead and unplug the TV for a few minutes, then plug it back in. Sometimes these issues are just "glitches" that can be cleared by removing power.
If this doesn't remedy the issue, you definitely have an internal failure here. The good news is that everything is reparable; it will boil down to cost. So the real question is: Will repair be cost effective? The answer is... maybe.
There is a short list of possible malfunctions including the power supply, the main board, the scan drive or sustain boards... or even the plasma panel itself. It's tough to say for sure without making any measurements inside.
So if the unplug doesn’t cure this, consider having a tech take a look. Some diagnostics shouldn't run more than $50-$75, but that would be put toward the final bill should you decide to have it repaired. A typical repair here would be $250-$550, unless it's the panel... then repair would not be cost effective; a new panel is far too expensive.
If you'd like, feel free to post back here with your zip code and I'll see if I can find someone close by, ok?