So I tried to connect my Google Stadia controller to my phone but it was said it was connected and yet it wasn't so I held the power button on the controller to turn it off and when I tried to turn it back on it wouldn't do anything so I plugged the charger in and the light didn't even come on. If anyone has had this issue and found a solution please let me know.
You can try the following simple steps and this may fix the issue.
1. Put the controller on charge for 30 mins
2. Unplug the controller
3. Hold the Stadia button for 12 seconds
4. Press the button as you would normally.
5. If this does not work put the controller back on charge and press the Stadia button
If this does not work you should then contact Stadia and they may be able to help you further.
Source: https://stadiasource.com/article/596/What-to-do-if-your-Stadia-controller-does-not-power-on