Few things to try:
* Verify that your phone has a sufficient charge.
* Connect your original charger to your phone.
* After a few minutes, try to turn on your phone. If it doesn't work, try another charging cable. Try mains and USB charging.
* Verify that your phone, charging port, and battery contacts are not damaged.
* Carefully inspect your phone's charging port and remove any debris.
* Remove the battery.
* Carefully clean and inspect the gold contacts on both the battery and on your phone.
Attempt a forced restart of the phone.
* Press and hold the Power key for 30 seconds.
* If the phone starts to power on, release the Power key.