Start by properly and completely identifying your mac. Then study the guide and see if you are capable of this DIY (this is a major task). Order the proper tools (every job is easier when you have the proper tools) and replacement logic board.
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2 GHz Motherboard / Ports: Mini DVI Video Out, 1000BaseT Ethernet, Firewire 400, 2 USB 2.0, Audio in, Audio out — 5 available at 169.95 each.