TV turns on, but a picture from previous channel I was watching is frozen to the screen. I've unplugged cable cable card and connection to cable service and picture is still frozen on screen. Will not power off by remote. Only powers off if I hold power button down on TV.

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Reboot your cable box first by unplugging the power for about 30 seconds

Try turning off the cable box at the mains, by unpluging the plug.

have your tuner check for any cold solder on pins.

I also have a Brand new Sony Bravia 52" LCD with Comcast Cable (motorola box).When switching between HD Channels sometimes the left side of the screen shows a smushed version of the new channel, and the right side is a frozen picture of the previous channel. I correct this by switching to a non HD channel and back. Cable or TV problem I wonder?

hook up your sat/cable box and reset the tuner; place the set into "setup" then: "add channels" the tuner will look for and install active channels

Try One of your working TVS and connect it to your cable outlet of the TV that is having problems. If that TV Does not work then there may be a degraded fitting or the Leg coming of the splitter to that outlet could have a Low Signal Problem
Next Take the First TV that was not working properly and put it on the cable outlet of one of the TVs that is working properly and if the TV set works on that Channel then you know it is not your TV that it must be the cable

If you have static siugnal, sure TV is not dead.

Check the aerial cable, ensure it is well plugged in and getting signal.

If you are using a receiver box, check cables to TV and receiver (freeview, sat, cable etc.), try setting channels on receiver again, if it does not work but you get static, then either the cables or receiver are defective.

Test the TV on standalone , connecting it to an external antenna.
Tune again the channels, and save the preset.
If still no signal then the antenna socket on the TV may be defective.

Try using the TV with a DVD.

If you can watch DVDs, and TV is not keeping channels preset, and you tried all the above, at this point htere may be a fault in the tuner card inside tv.

Call the phone number listed on tv user manual to get support, and eventually repair it.

The aspect ratio (zoom) button on the cable remote had been changed. On Brighthouse the # button toggles through the zoom settings. It's not a tv issue, it's a cable fix.

Sounds like the PIP feature is causing the problem with the TV if you are connected directly to cable TV without a box inline and getting these issues.