Power Mac G5 not booting.

Hi & a warm welcome to the Forums & Macdom! 🙂

Without an OS to control the Fans it's normal for them to go into high gesr for safety.

You might get some bare useless video with one of these boot options...

Hold the Option/alt key at bootup.

Does it boot to Single User Mode, CMD+s keys at bootup, if so try...

/sbin/fsck -fy

Repeat until it shows no errors fixed.

(Space between fsck AND -fy important).

Resolve startup issues and perform disk maintenance with Disk Utility and fsck...

http://docs.info.apple.com/article.html?artnum=106214

Might be time to replace the PRAM Battery, 4 years is close to their lifespan, far less if ever without AC power, & can cause strange startup problems...

See which one your G5 has...

http://eshop.macsales.com/item/Newer%20Technology/CR2032/

http://eshop.macsales.com/item/Newer%20Technology/BAA36VPRAM/

Still, without an Install Disc, you're up a creek, G5s can run 10.3, 10.4, or 10.5, trouble is finding a reasonally priced version of the Retail versions, since Apple no longer sells them. 🙂

Was the machine supposed to have been running before you acquired it? If not, then we'll start at the beginning.

When a G5 powers up, the white LED over the power switch should come on when the button is pushed, then as things get started, it should stay lit. The fans will want to run up to full speed, but initially the PMU or SMU will ramp those fans back down and start a watchdog timer which is reset periodically by the operating system when fan control commands are written to the PMU or SMU.

Since the fans are not ramping down for a little while, that is first suggestive that the PMU or SMU is not coming up. The first thing you need to do is to verify the PRAM battery condition, as a weak battery can cause all sorts of mischief. One does that by measuring the voltage on the battery while in its holder with the AC power disconnected from the computer. The voltage should be somewhere between 3.3 and 3.7 volts. If it is below 3.3 volts, the battery needs to be replaced.

If the PRAM battery is OK, then you need to try a PMU or SMU reset (information at links). For the machine you describe, I believe the SMU reset is what you need to do. If the management unit is successfully reset and actually working, you should now have the machine power up and at least the fans should come down for a little bit. Since there is no OS on the machine, what should happen is a boot tone (chime) sounds, the video comes up and then there should be video with a folder and flashing question mark appearing, indicating no bootable OS was found.

Not saying that the above guarantees success; it's just that those are the first steps that need to be taken to see if the machine can be revived.

"unit shows slight signs of life"

Not a great thing, especially with a G5! 😟

Do you have another Mac around with Firewire, or an enclosre you can pull the Hard Drive out & we can try to inspect the system.log for possible clues if there are any?

So sory to hear your first Msc experience is going so badly! 😟

Is there at least one red LED lit up on the Logic board if you open the side panel whike plugged in?

Does the Power button light up when pressed? Does it pulse/flash?

Well, the logic board seems to be getting some power for that LED anyway, could be that little power button, or can you check voltages?

Pin 14 is PWRON, and...

https://discussions.apple.com/thread/2612757?start=0&tstart=0

https://discussions.apple.com/thread/2519755?messageID=11980210#11980210?messa geID=11980210

OK, good idea on the return, good luck too! 🙂