@andyc7117 start by trying to reset the PMU:
After that I'd try to change the logic board battery.
"Logic Board Battery
Important: Apple highly recommends removing the battery when handling the logic board. Make sure to use proper ESD protection when handling modules.
The battery on the logic board controls the stored system settings, such as date and time. It is only necessary to test the battery when you can’t power on the computer, or the date and time are reset every time the AC power is removed.
The battery is also used to power the PMU chip (because the PMU chip keeps time and must always be running) when the computer is unplugged from the wall (AC power). The PMU is very sensitive and touching any circuitry that is connected to the PMU can cause it to crash. If the PMU crashes, the battery life goes from about five years to about two days if the PMU is not reset. Once the battery goes dead, the PMU will reset the time and date to 12:00 AM 1/1/04 every time the AC power is removed. To fix this situation, replace the battery and reset the PMU (refer to “Resetting the PMU on the Logic Board” mentioned earlier in this chapter).
If the computer has a “No Power” situation, check the battery before replacing modules. A drained battery may be indicative of a crashed Power Management Unit.
Does the battery measure at least +3.5v? If not, replace the battery and reset the PMU. If the battery does measure over +3.5v, reinstall the battery and reset the PMU as above.
Connect the power cord and power up the system again.
Warning: Whenever the bottom housing is opened for service, you must do two things:
1. You must clean and reapply thermal paste to the thermal pipe surface.
2. You must tighten the four torx bolts on the base unit to a minimum of 17 in.– lbs. Failure to follow either of these steps could cause the computer to overheat and damage internal components.
Here is the No Power trouble shooting section:
The computer will not power on.
1. Verify the power outlet is good. Plug a different device into the socket to ensure there is power, or plug computer into another outlet.
2. Check the power cord. Use a known good power cord.
3. Check connection of the power cord on both ends. Verify that the plug is securely plugged into both the A/C outlet and back of the computer.
4. Remove keyboard, mouse, and other peripherals such as speakers.
5. Disconnect the power cord, place the computer in the service stand, and remove the user access plate.
6. Reset PMU. Refer to “Resetting the PMU on the Logic Board” mentioned earlier in this chapter or Kbase article 95165.
7. Verify the battery is good before replacing modules. A drained battery may be indicative of a crashed Power Management Unit. Does the battery measure at least +3.5v? If not, replace the battery and reset the PMU. If the battery does measure over +3.5v, reinstall the battery and reset the PMU.
8. Connect the diagnostic cables (part 076-0897) between the upper housing components and the logic board. Refer to “Service Cables” mentioned earlier in this chapter. Important: Diagnostic service cables allow the unit to run while the bottom housing is open (as shown above). However, the computer cannot run for more than five minutes with the bottom housing open. If it is open longer, the CPU may overheat
and become damaged.
9. Check the connection of the video cable on the LCD flat panel, and try to power on the unit again.
10. Check the AC line filter. To measure power at the AC line filter cable, disconnect the AC line filter cable from the power supply cable. Switch your multimeter to read AC voltage. Touch the black probe to the pin of the brown wire, and touch the red probe to the pin of the blue wire (see graphic below). Do you measure 120v (line voltage)? If yes, go on to step 11. If no, replace the AC Line Filter.
11. Check power supply output. Disconnect the diagnostic power cable from the power supply connector, and measure power at the power supply connector by touching the black probe to the ground pin, and using the red probe to measure power at the pins indicated in the graphic below. Did you measure +12v at each point? If yes, continue with the next step. If no, replace the power supply.
12. Check the main logic board voltages. Measure for +12v DC at capacitors C187 and C197 (identified in graphic below). Ground the black probe to the logic board screw next to the battery, and touch the red probe to the positive node at capacitor C187, and then at capacitor C197. Do you measure +12v? If yes, go on to the next step. If no, replace the logic board.
13. Replace power supply.
14. Replace the logic board.
15. Replace the inverter board.
16. Replace neck assembly.
Let us know if that changed anything before trying to replace the parts listed in step 13-16