sorry to hear that. There would be two ways that I can suggest.
First of all, keep the ON/OFF button pressed for 20-25 seconds while connected via USB cable to your PC. Open a Explorer Window to see if it appears.
The try to switch it on by releasing the button and pressing it again for 3-4 seconds.
If this should not work, you can re-flash you mobile. Please let me know, if step one has helped already.