Won't boot, but fans and front panel light is on

jerryfischer24 let's check a few things first. Using the troubleshooting guide from Apple

No Video

The computer will turn on, but the display has no picture or color. The boot hime, the fan, and hard drive activity can be heard.

Check if the computer is sleeping. Press the space bar to wake the computer from sleep mode.

Did the computer wake from sleep?

Yes: Put the computer to sleep from the Apple menu and wake the computer again to test the settings. Check the Energy Saver setting to see when the computer has been designated to sleep.

No: Continue to the next step.

Reset your computer’s PRAM (Parameter RAM).

- If your iMac is on, turn it off by pressing in the power button until the computer powers off.

You should hear the drives and fans go quiet.

- Wait for a few seconds.

- While the computer is off, with your left hand, hold down the Apple key, the option key next to it, and the letter R. When you have them all pressed push the power button with your right hand and then quickly move that hand to hold down the letter P. Keep the four keys pressed while the computer starts up.

- Make sure you hold down the four keys (P-R-Command-Option) while the computer starts up. When you keep all the keys held down, you will hear the startup chime over and over again (about every ten seconds) until you let go. After you hear the second chime, you can let go of the keys.

- If you didn’t hear at least two startup chimes, go to step one on this page and try again. It’s important that you hear two startup chimes when performing this procedure. This indicates that you have successfully reset the computer’s PRAM (Parameter RAM).

Does the computer display video after successfully resetting the computer’s PRAM?

Yes: Problem resolved. Restart the computer from the Apple menu and make sure the computer is starting up properly.

No: Continue to the next step.

Remove the access door, front bezel, and lower EMI shield to access the diagnostic LEDs on the logic board. Refer to “Accessing the Diagnostic LEDs” earlier in this chapter.

Locate diagnostic LEDs 1 through 4 on the logic board.

Plug the power cord into the iMac G5 and into a known good AC outlet. LED 1 should come on if your computer has been starting up properly. If LED 1 is Off, refer to the “No Power” troubleshooting earlier in this chapter.

Turn on the computer by pressing the power button.

When the computer starts up, LED 2 will light, indicating the power supply is functioning properly. If LED 2 does not light, refer to the “No Power” troubleshooting earlier in this chapter.

LED 3 will light last, indicating that the logic board and LCD display assembly have communicated and the display is ready to receive video. Does LED 3 come on?

Yes: This indicates that your logic board is working correctly to produce video. Continue to step 12.

No: Continue to step 11 to reset system power management.

Reset the SMU (System Management Unit). Refer to “Resetting the SMU” mentioned earlier in this chapter. After resetting the SMU, did the video return?

Yes: Press and hold the power button until the computer powers off. Start the computer again and confirm that the computer is functioning normally. Continue to step 14.

No: Go to the next step.

Connect an external display. Does the external display display an image?

Yes: This indicates that the logic board video circuitry is functioning properly. Continue to step 13.

No: This indicates that the logic board video circuitry may have failed. Replace the logic board and retest.

Turn the display at an angle to you and look closely at the display. It may be necessary to dim the room lights. Is the display completely black, or can you see a dim light or purple glow to the display?

Completely black: Replace the inverter.

DIm light or purple glow: The inverter and LCD backlights are functioning. Replace the display panel and continue to step 14.

Turn the machine off by holding the power button until the unit powers off. Unplug the computer and reinstall the EMI shield, front bezel, and access door. Return the computer to the upright position. Plug in the computer again and power on the computer.

Does the computer have video now?

Yes: Restart the computer and make sure that the computer is operating properly.

No: Return to step 1 to verify system functionality.

Again, this is most likely just a start. The G5 had some terrible issue with capacitors failing. I do suggest that you take it apart according to these guides iMac G5 17" Model A1058 Then carefully clean the parts and evaluate all of them carefully. After all, you are dealing with a 20 year old piece of electronics and you need to evaluate any potential damage first.

Post some good pictures of what you find/see with your Question. That way we can see what you see. Agregar imágenes a una pregunta existente

Here are a couple of documents that will come in handy for your repairs etc.

IMac G5 Repair 1IMac G5 Repair 2IMac G5 Repair 3