my phone has been charging for hours but still wont turn on

If the battery is dead, no amount of charging will push enough juice to start the phone. You will have to take it in for assessment whether it is the battery or something worse. And what options you have for recovery.

Try a different charger and/or cable. If it's been on the charger for hours and won't start then something is wrong with either the phone or charging system. If you have an iPod or iPad that can connect to the same charger, that would be a good place to start testing the charging system.

It is probably in DFU (device firmware update) mode. If that's the case, while it's plugged in, hold the home and power buttons at the same time for about 20 seconds, then let go. Hopefully that's the problem and not the battery.

Your phone probably died.

Time for a new one.

try holding the power button and the home button down at same time for 10 seconds

if that doesn't work connect to power and hold power button down and home button down at same time for ten seconds