you can replace the display assembly on a nokia n9. all steps are detailed in nokia service manual.
most of the time a nokia n9 that will not turn on is due to a discharged battery. you can force charge it by using flasher utility.
start the flasher utility, then plug your device and do nothing else but wait. this is a trick to force charge of a nika n9 battery was discharged too low. consider replacing the battery if this happens often.