Press the power button a very long time... Til phone vibrates.

And are you sure its charged?

---------- Post added at 10:49 PM ---------- Previous post was at 10:47 PM ----------

And did you unlock the bootloader? If its not a dev edition, unlocking bootloader voids warranty.

---------- Post added at 10:49 PM ---------- Previous post was at 10:49 PM ----------

As does flashing other carriers firmware I suspect.

But, maybe you'll get lucky!

Good luck!
Sent from my new HTC One M8, N7, Moto X, GTab3 or S2.

Need help with poor battery life? Any device welcome, even tho its an N5 thread. Please specify if on a device other than N5. Lots of info in first 4 posts! >>>>
[Battery Life Help] Troubleshoot Battery Issues Here....and Tips