If you unplug and hold the power down, that's just giving the tv a "refresh", like turning your computer off an on again. The reason you hold the power button is there is still power left in the capacitors, and it's quicker to hold the power button than to wait an hour. You should not lose any settings by doing this. Actually, I've had mine unplugged for days and not lost settings.
If that doesnt work, you can try a full factory reset. Hit menu, go to setup, go to factory reset (or system restore, not sure exactly what it's called). This will reset the tv to factory, and should clear up any software issues. You will lose settings, but it's water under the bridge if it fixes your problem.