Dual 2.5 G5 Won't Boot. Fan's just go to 100%

[TwitchOSX]

Dual 2.5 G5. Been having a similar problem to this for about 6 months now. After I reboot it (or there is a power outage), when I turn it on, I get black screen, no chime and the 2 rear fans slowly spin up until they sound like they are running at 100% each. It's like a jet engine in here!

Previous fix was to hard reboot (hold the power button for a few seconds to shut down and then hit power button to turn on) and then it would boot up normally.

This morning I came in and both fans are running full bore. Nothing on the screen. I figured we had a power outage over the weekend and when It restarted itself this happened. However, from looking at the other computers, there doesn't appear to have been a power outage. Also, that machine normally shouldn't have started itself back up anyway so not sure whats up.

I've hard rebooted it several times this morning and I get all the same stuff. I don't know where the discs are that came with the machine at the moment but any ideas?

It's running 10.5.6 or something like that.

 

[TwitchOSX]

Update:

Command - Option - P - R on boot does nothing

Command - Option - O - F to boot into Open Firmware does not work

Power is on, but the power light on the front above the power button is not on.

Fans are starting to spin up to 100% after that last reboot a minute ago.

 

[TwitchOSX]

Update 2:

Pulled 4 of the 8 ram sticks out. Not sure which came with the machine or not but pulled those, pulled and put back in the video card... same stuff happening.

Put in the Hardware Test DVD (or CD.. whatever it is) and tried to boot from that by holding down the C key on boot and nothing happens.. well.. same stuff happens, which is nothing and then the fans go crazy.

 

[TwitchOSX]

Update 3:

Tried hitting the PMU Reset button by the ram chips and that didn't help. Pulled some more ram so I only have 2 total ram chips in and that's not helping. I pulled one of the hard drives out and put it in this Mac Pro and that is working fine.

 

[Lil Chillbil]

It could be a blown processor or that the motherboard is not properly plugged in

 

[Goftrey]

Same thing happened to my uni 1.6 G5 - the only thing I could think of is a knackered logicboard. It's pretty common on the G5's, you've got a dual 2.5, which also seems to be one of the more unreliable G5's (mostly down to the LCS though I guess).