Probably the connector/mainboard is corroded - or the chip on the mainboard is fried.
This might help:
http://www.ifixit.com/Guide/Discuss/thre...
[quote|EdNem]Probably the connector/mainboard is corroded - or the chip on the mainboard is fried.
This might help:
http://www.ifixit.com/Guide/Discuss/thread/1487[/quote]