Flashes an apple logo and goes blank when connected to power

My have just changed the mother board of my ipad 5 and unable to boot it up. It was lying for a long time with a broken motherboard and the battery could not be charged. Now when connected to power, the apple logo flashes for a moment and the screen goes blank with a dull lighted background. Pressing the sleep/wake button for few seconds switches it off momentarily. After this the logo appears again for a moment with the screen going blank again. It is not possible to switch it off. Home+sleep/wake button combination does not do anything. Is it a dead battery situation or something else needs to be looked into ? The situation is like this even after keeping the charger connected to power for more than 8 hrs. Thank you for any suggestion/feedback.