Why TV is restarting?

@ilar you say it restarts, does that mean it turns all the way off, then starts up showing the Samsung splash screen on startup etc.? Your TV is a model UE46ES6800?

Since you can resolve it by "knocking it's back it will be ok "the issue appears to be related to your power supply or the power cable. Unplug your TV and remove the back cover. Then take a look at the boards. Check for any odd, charred or missing component. Check the wires to ensure those are all properly seated.

Take some well-focused images and post those with your Question. That way we can see what you see and hopefully find the issue.

Adding images to an existing question - iFixit Repair Guide