Cold booting your TV is a little different than simply turning it off and back on. When you turn it off, it is really in standby. A cold boot actually shuts the TV down and reboots it, like restarting a laptop. This can solve issues you may be having with apps, glitches in the menu, picture issues, etc.
There are two ways to cold boot your TV.
With the Remote: For most people, the easiest way is to hold down the Power button on the Samsung TV remote until the TV turns off and on again. This should only take about 5 seconds.
With the Plug: If you do not have the remote, unplug your TV from the wall outlet or surge protector, leave it unplugged for 30 seconds, and then plug it back in.
If you switch off a surge protector with other devices plugged into it (such as your router), give them time to power up and reconnect before testing any functions on your TV.