Q: iphone is not turning on

Are you sure the device is charged? If so, then hold the sleep/wake and home buttons together until you see the Apple logo and then release. The phone should reboot. This can take up to 30 seconds of holding. If you are not sure if it is charged, then plug the device into the charger for at least an hour before attempting to start it using the method I describe above. Not sure why you are trying to use DFU mode just to turn on a device. Kind of overkill I would say.

If the force restart did not work, then follow the other steps in this support document. If your iPhone, iPad, or iPod touch doesn't respond or won't turn on - Apple Support  The last step is to contact Apple Support.

sameee