ndwig , here is the way Apple suggest that you check this particular symptom:"
System is completely dead (no fan movement and power LED is not lit)
1. Verify the power outlet is good.
2. Replace the power cord.
3. Make sure the voltage switch on the back of the power supply is set to the correct
4. Reset the logic board. Refer to “Resetting the PMU on the Logic Board” in this
5. Check for trickle voltage on the power supply connector. Refer to “Power Supply
Verification” in this chapter. If verification fails, replace the power supply.
6. Disconnect external devices, including the monitor, and start up the computer.
7. Remove internal cards and start up the computer.
8. Disconnect internal hard drives from the logic board and start up the computer.
9. Check the modem connector. If the connector has any bent pins, replace the logic
10. Check the pins in the power supply connector on the logic board. If the pins are bent,
replace the logic board.
11. Replace the logic board.
Hope this helps, good luck.