My Sony Bravia KDL-40S2000 turns itself off automatically after about 2 minutes and the stand-by light blinks 4 times

Please unplug tv from wall socket for minute or so,, replug back in and turn it On.
If tv still goes to standby itself than its standby light would blink to show an error in somewhere inside tv circuits.
Let me know how many times standby red light blinking? There would be 3 seconds long pause in blinking so count pause to pause to determine problem section.
Thanks.

That error says backlight failure. It has to be troubleshooted to find out why.

Ur power supply board it dying will be dead,must replaced.

I would suspect one or more of the miniature flourescent backlight lamps. One way to confirm this would be to power up the set with a grayscale image at 40 to 60 IRE. If one or more lamps is failing to light, a slightly darker horizontal area in the grayscale will give it away. Unfortunately, Sony will not supply any of the backlight components apart from a new LCD panel. Sorry.

4 blinks is bad backlight inverter. Download the service manual here:

http://rapidshare.com/files/208591107/KDL40S2000_L5_sm.pdf

turn off the sleep mode in menu/settings

It has a faulty power supply or processing boards. Must take to agents to sort out. Nothing you can do on the outside.

Replaced circuit board under warranty.

You will have to contact sony customer support. The 13 blinks indicates a balancer bad. The balancer is part of the LCD panel. The Tv can'[t be much more than a year old. The panel will require replacement. Sony will probably direct you to an authorized servicer. Let me know if I can be of further assistance

Sony are normally pretty good,you just got unlucky i guess,well at least you still got the warranty.