wont power on, flashing windows logo?

Replaced screen assembly, upon charging to test, it will not power up and the only response from plugging in a charger is the windows button flashes repeatedly. I have read that that means a severely drained battery but that is not the case here as i left it charging for 8 hours with no change. Also cleaned contacts and tried unplugging and replugging battery. Even tried windows software recovery program but the phone will not connect to the computer. Also tried a soft reset. Help?