Dell Latitude D600 issue

I just replaced a broken LCD screen on my D600. It was working with the cracked screen but you could barely see anything. I got the same exact screen (make and model) as the broken one. After I replaced it I went to charge up the battery as it was unplugged for awhile and the green light on power adapter turned off as soon as I plugged it into the laptop. I've read about other people having this issue and the motherboard has gone bad. Just wondering if anyone has any other suggestions. I tried different batteries, power cords, I even removed the battery and tried to run straight off AC power, but no luck.
Any help will be greatly appreciated.