Mac Pro 3,1 turns off straight away after power button press

It's quite difficult to phrase this in a concise way hence the longer title then I would have wanted. Basically, I have a Mac Pro 3,1 early 2008 model, which, when the power button is pressed, a fan turns on, power light comes on, and within 1 second the shutdown click is heard, fans turns off and power indicator light switches off.

After this, the power button does not do anything when pressed unless you wait at least 1 minute.

I tried a few different things at first which did not resolve the problem:

• unplugged everything, waited 30 secs, plugged it back in again (SMC reset)
• took out the Hard Drive
• took out the RAM
• took out the DVD drive
• took out graphics card

Finally I thought I'd look it up and found this post and this post which both described the symptoms perfectly, and all answers pointed to a power supply problem.

Thought I'd check this out, but needed some instructions on how to get the power supply out. Found this scribd.com manual which did the job. Looks like an official manual.

After taking it out, I cleaned it up with a can of air and put it back to no avail. Next I tried swapping with another out of a Mac Pro 3,1. The working one worked in the previously not working machine, and the broken one didn't work in the working machine (is that a good way to put this?).

So, conclusion, the Power Supply Unit is not working correctly. Reading the manual further I found that it looks like the "trickle feed" isn't working correctly.

Apple Part Number: 614-0409

Looks like a new one is about £280, or refurbished is £105 from USA.

No preboot keyboard shortcuts working on White iMac 17" and 21"

We've had both 17" and 21" white iMacs for about 5 years and in that time I've re-imaged them at least 5 times (once a year) using NetBoot (hold down "N" on preboot). But recently I've noticed that these iMacs no longer register any pre-boot shortcuts including reset PRAM ("alt" + "cmd" + "p" + "r"). This means if I have a problem with them (i.e. if the hard disk fails) I won't be able to work any magic on them. Luckily I've not had any trouble yet but in time it'll need sorting out.

I originally assumed it was the last image i'd put on them, or the way in which I'd done it but noticed, but I didn't think that would effect anything pre-boot, like firmware.

I've done a few searches and found mostly mentions of Bluetooth/Wireless keyboards having this issue and one mention of 3rd party keyboards, but no real success finding anyone with this particular problem. I did a few more searches and found this which does sound more promising. The only difference being it does holding down "c" and "alt", but I didn't try these as I just assumed they would work after trying PRAM reset and "cmd" + "s" single user mode. (Never assume anything!)

A person down the bottom says the PRAM battery might have failed, which would make sense as they are over 5 years old and are unplugged for large periods of time (for security measures). The next question: How to replace battery in old white iMacs?

For the time being I shall just have to rely on them working and use the system prefs to alter startup disk.