How do you fix your ipod if it won't turn on?

It is different for each model of iPod.

If you have an iPod Touch you hold down the home button (with the white square on it) and the power button on top at the same time until you see the Apple logo. Once you see the Apple logo IMMEDIATELY let go of the buttons otherwise you will put it into recovery mode which is something you don't want if it just won't turn on.

If you have an iPod Classic/Nano you hold down the menu button and the center circle button at the same time until you see the Apple logo then let go once that comes up.

If these don't fix the issue and you have already tried things such as charging your ipod on a different computer or a different charging cable, then I would call Apple Care Technical Support at 1-800-275-2273 or your local Apple Store.