sound like the pixels have gone out. being that it's a 7000 series it might be time for an upgrade anyway. without seeing the screen though. it's not possible to know what actually happend
When that happens usually is called screen burn-in which is caused by wear/high brightness. If your TV is within warranty I suggest you replace it immediately, or get another TV. Sadly there is no way to fix it (without overpaying the price of the TV). Google luck, stay safe.