I'm sorry to hear that you're having this issue. But I think we can help you out here.
What's happening is that your television is in SHOP Mode. There are two modes: Shop (or Demo Mode) and Home Mode. When people mess with the settings in your average retail store, this feature is designed to return the television to the factory defaults between 10-30 minutes. So what it sounds like is that this was activated on your set.
Now, there are a few ways of handling this for your three year old unit. Since I don't have a model number, I'll give you two suggestions that should work. If not, post back the model number and I'll be able to be more specific.
But try these for the 3 year old model:
1. With the TV powered ON, press and hold the MENU button on the bezel (border) of the television (not the remote). The screen should blink and either say Home Mode, or Standard Mode. It also might say Dynamic mode. Change the brightness and contrast both to 100, turn off the set, and power it back on. If the brightness and contrast are still at 100, then you are successfully out of Shop Mode and you can set your TV and it will stay.
If you have small children or a habit of holding down the MENU button on the TV for periods of time, that may re-activate Shop Mode.
2. If that doesn't work, the second way is very similar. But before holding down the MENU button for 15 seconds, press and release the "increase volume button" first, and then press and hold MENU while the volume indicator is still on the screen.
Then test it by turning your brightness and contrast to 100, power off the TV, and then power it back on and see if those settings stick.
Okay, so now for the TV with AutoMotion Plus, go to the TV input using the remote, then following these commands with the remote:
MENU (button on remote) > SETUP > PLUG AND PLAY > Right Arrow > [Enter]
You will be prompted to do a channel scan just like the day you bought it. But it will give you an option for Store Mode or Home Mode. Select Home Mode, and you'll be home free.
Keep me posted, and let me know if this helps you.
I have two Samsung LCDs. One is a 40", about 3 years old. After about two years, every time I turn the TV on, all the settings on the TV are just as they were when I first bought the TV. Even if I change the settings, after about 10-15min, the TV goes all black and then when the picture comes back on, its back to the default settings. I learned to live with it, since I almost didnt use that TV. I bought another Samsung LCD TV 50" about a year and a half ago, and about a month ago it started doing the exact same thing. I tought the 40" did it because it was a little old, etc. But this brand new TV started doing it aswell, and its my home theater TV, so its getting very annoying. This bothers me a lot, since I hate the look of the "Auto Motion Plus" (120hz), and also like to watch my movies in the "Movies" setting, not in the "Dynamic" settings. Even if I change the settings, after a couple of minutes the TV goes all black and comes back on on its default settings. Any help anyone? I really want it to stick to the settings I put on it.
Thanks in advanced!