I'd be willing to bet that you have just unpluged the power to plug into your new head unit, this is why you have no power to it, when installing a new headunit you need to split the power, its not as simple as just removing the iso block and sticking it in something else.
Easy way for you to check is unplug the new head unit and plug it into the old one, bet it all powers up again.
hope that helps.