Hold down the power button and volume up until the name displays. Release the power button and hold it down again. This will allow you to factory reset the device and should then turn on. If not the screen could be fried.
Are you using the Gear 360 (2017)?
If so, just confirming that you are holding the lower button on the side to get it to turn on? It has a red icon with an exclamation mark. That is the power button. The big button on the front is not the power button.