Doesn't do anything

Hold both buttons down until the Apple logo appears and then let go of

both. Sometimes can take 20 seconds or more.

If still not starting, look here:

If your iPhone, iPad, or iPod touch doesn't respond or doesn't turn on - Apple Support

Try getting it into DFU mode and restore it. If you dont know how, visit this site https://www.theiphonewiki.com/wiki/DFU_Mode.