Same symptom. All seemed to go well with the digitizer replacement but no response to power-on switch. But when opened up again found that somehow when reassembling I managed to tear the power on/off ribbon cable! It boots by inserting a usb (charger, sync) cable into the phone while simultaneously holding down the Home and Volume Up buttons. So I just put shortcuts to the Widgets: Screen Off, Airplane Mode, GPS Toggle, Bluetooth Toggle (energy savers) on the Home screen and keep the phone on the whole time. ['Just have to remember not to remove the battery without having a (phone-)USB plug nearby.] I got the replacement switch on eBay but not sure my (de)soldering skills are up to this delicate task. (More damage?!)
The demo ends before it does what is stated in the heading (Display Replacement.) This demo is for Front Panel Assembly Replacement.