I usually let it cool down then hold the down the top button and the front button down at the same time until it comes on. If that doesn't work then I hope your still under warrnaty, you can check here..
https://selfsolve.apple.com/GetWarranty.do
Its the U.S. site but probably same general area if your not in the U.S.
I called the support line and I am taking it in today to hopefully get replaced.
Sorry I couldn't be more help