Most commonly this is caused by a faulty control board (the board with all the buttons on the front of the TV) however it can be caused by a faulty micro as well, the first thing I would do is attempt to clear the EPROM of corrupt data heres how you do that:
Turn the tv on so you have a picture
While it is still on unplug it from the wall
Let sit for 10 minutes
Plug it back in and see if the symptom is better.
If the reset does not work and the control board is found to the failure then unfortunately the way to repair this is to replace all the switches on the control board, this is done by unsolder and re soldering all the new switches in. A repairman will do this for $175-$225.(unfortunately I know this is almost as much as the set.)
There is the possibility that the micro on the tv it acting up as well, if this is the case then most likely the main board would need to be replaced if the reset did not fix the problem.
Please let me know if you want to try this yourself, or if there is anything else I can do for you!
If you would like any additional information or have more questions please don't hesitate to ask!
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