Hello and thank you for visiting us!
IF you have a phone that you can remove the battery, then do so. While battery is out, hold power button down for about 3 seconds. Now, replace battery, and power up, hopefully.
One other thing....plug device into wall socket and monitor it closely for about 5 minutes, to see if it comes on. If these thing don't work, then I"m afraid a trip to the repair center is in order.
CHris