Tv TURNS OFF BY ITSELF AND NEEDS TO BE RESET BY THE MAIN POWER BUTTON

Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electro-medical.blogspot.com/
http://electronicshelponline.blogspot.com/
In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.

test with your cell phone directly then reconnect the modem last reset tv to do so in main menu

You have main board issues, there is a 3.2 volt regulator on your TV that gives issues and will make the set turn on at random times, replace the main board and it should fix it, or you can order the part for under a buck from China and replace it yourself if you have soldering skills

Main system control memory IC fault. This is a very small IC; have 8 solder terminals, and can be located very near to the main system control-chroma IC. Check and replace it. Be sure to replace it with the same number printed on it; in all respect. Otherwise, it won't go. http://electronicshelponline.blogspot.com/ Before replacing it, try a reset to this set, and then check.
There are two methods to reset TVs. The first is simple to do; a Hard Reset. The other is somewhat skilled; is a Factory Reset (System Reset). To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. If you do this by overnight is better. This procedure will make it a hard reset. If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option. If you wish to get some details; check the site linked here.

Check the standby timer. Or reset your HDTV to factory settings. Just turn on the TV. While holding down the RESET button on the remote control, press the power button on the TV. (The TV will turn itself off, then turn back on again). Release the RESET button..

Most likely a blown capacitors. Take off the cover and examine the capacitors on the main power board. If they are bulging or leaking they need to be replaced.

YOU WILL HAVE TO REPLACE THE POWER SUPPLY IN THE TV

You have a bad Main bd. Have a trained Samsung tech repolace the Main bd.

Symptoms of a Defective or dying Power supplies on LCD TVs.
1. Light(s) on the front panel are behaving not normal example, blinking, amber color or
not steady, fainting, etc.
2. TV not turning ON properly.
3. TV turns OFF by itself.
4. Needs to be unplug to many times to make it work.
5. Humming or high pitch noise heard through speakers or at the back of the TV.

This usually means that the TV was last shutoff by using the sleep timer. When that happens it usually needs to be turned on and off 2 or 3 times, or try using the main power button on the tv or simply unplugging it. A full reset probably wouldn't hurt either.