If this is still helpful,
Remove the rear cover of the device and the frame till you can see the board. In the location where your power button was, there should be 3 gold pins on the main board. Bridge the two lower ones and your device should start. Sometimes I use anything metallic and touch it across the two pins and sometimes I just let my finger touch them simultaneously, the power in them is almost 0.
If this doesn't work then your device likely has some board damage. Try combinations of the different pins if it doesn't work for you, I don't know if there are differences in the models.