Hold down [Enter] and [Mode] while quickly pressing the [Power] button (DO NOT HOLD THE POWER BUTTON, just a quick press).
Continue to hold enter and mode for a few more seconds.
You should see the screen barely flicker on when you push power, and then nothing else should happen until you release the enter and mode buttons.
After you release the buttons, your unit should power up and go through the initialization screens.
Since this can be a difficult sequence to do, it is best to keep trying a few times if it doesn’t work at first.
This worked for me and I didn’t have to reset the unit. Looking at the Garmin forums a lot of people are having this issue after a first charge.
Unit not responding to Button Presses?
Say it’s on but it won’t respond to presses, press [Mode] and [Lap] simultaneously to reset the unit.