There could be a couple of reasons for the phone not to turn on. Try turning your phone on, by pressing the power button for 7 seconds. If this does not work try to charge your phone. Connect to a charger and let it charge for a 30 minutes and then try to turn it on. As simple as it may see check that the charger is plugged to the wall. If all these don't seem to work, it could be possible that the battery is drained. Try to replace the battery. See Replace Battery Guide