If Alexa isn't turning on your Samsung TV, there are a few possible causes. There may be an issue with the SmartThings app, so check your SmartThings settings and make sure everything is working correctly. If you're using an Echo device to control your Samsung TV with Alexa, make sure you're using a command specific to your TV. You can also try rebooting your Amazon Echo, removing the TV from your app, and then re-adding it. Also, make sure your Samsung TV is connected to your Wi-Fi network.