Tip - Mac Pro fails to boot up, no chime.

I don't think it would work if you remove the battery completely. You would need to replace it with one that was known to work, but this is just one of several areas to try. Also I think you need a minimum amount of Ram installed. Also I would remove the display if you haven't done so already.

I'll do that Ashley.

One other thing I forgot to mention was whilst pulling the power plug and plugging it back in during testing the Mac powered up without me having to press the power button on the front panel. Is this a clue as the what the problem might be?

How do you know if the processor is working?

1. Power off

2. Remove ALL the RAM

3. Power up normally

if the power light blinks a pattern of three, your processor is working. This is because those blinking patterns are generated in software.

Not sure about that business with all the starting up as soon as you attached the power cable. At the moment all sorts of crazy stuff could be going on.

One of the first things I did when I had problems was to install a different start up drive, which was a clean install of El Capitan with nothing else and remove all other drives. That reduced the risk of software problems and also allowed me to attempt dozens of restarts without risking damage to my main drive.

Have you tried starting from an external drive?

One of the simpler things you can do its to Alt/Option Boot. This draws a gray screen, even if you have no bootable drives. Then within three minutes shows an Icon for each potentially-bootable Volume. This code is all in ROM and it demands very little from your Drives to show an Icon.

Grant = thanks for that, I'll give the removal of the RAM a try and I'll try Alt/Option. So if the power light doesn't flash does this mean a processor issue?

Ashley - thanks, I have searched for installing ElCapitan on external HD. If I were to follow this procedure http://www.macworld.co.uk/how-to/mac-software/run-el-capitan-on-hard-drive-yosem ite-on-mac-3533305/ on my iMac would it then transfer bootable OS on ext hd for my iMac, or could I simply unplug and plug into my Mac Pro?

In my case I had a SATA on standby for emergencies of this kind and was simply able to slot it in place then remove the others.

You ought to be able to download OS X (any version is fine) on your iMac and simply set an external drive as the install location. You may even be able to do this on a USB stick. Then start while pressing the option key to hopefully select a drive connected to your Mac Pro. This won't be something you can do in 2 minutes but at least it could tell you if your drive is the problem. http://www.idownloadblog.com/2015/09/14/how-to-start-up-mac-from-bootable-media/

Something like this may work by using your iMac in target mode. http://apple.stackexchange.com/questions/153831/booting-an-imac-using-a-macbook- pros-internal-disk

At the moment we just want to hear that chime on the Mac Pro. In my case I couldn't reset the PRAM until the video card was removed. After the card was gone I reset the PRAM first time and it was all fairly easy apart from the cost of a new card.

Removed all RAM and inserted power cord. Again the Mac booted up without me having to press front power button. power light remains constant, no flashing.

Could it be a faulty front power switch panel? or is it the CPU board?

Hard to know for sure, but it might just be something related to that power button. I seem to recall there used to be a hardware diagnostic test that could be run, either by inserting some CDs that came with the computer or pressing the D key on the keyboard at startup. Have you been able to attempt a startup from an external drive?

I have tried every keyboard shortcut going. Nothing shows on monitor, still no chime.

i am currently desperately trying to create a bootable DVD, because the DVD drive of the broken Mac Pro does try to spin. Just having major issues trying to create a bootable DVD.

Went through the process of creating a bootable USB drive. After following instructions ended up with OS sierra installer on USB drive. I am now installing. Just need to transfer that onto DVD assuming I use ISO method...

I Still don't have a bootable DVD, after trying all night to create something bootable I just couldn't work out how to create a bootable USB drive or DVD. After installing I was advised to reboot and that my iMac may reboot a couple of times. This was a little worrying as I was concerned about my current OS on my fusion drive.

As mentioned in my previous post when I power up my Mac Pro I can hear the DVD drive, as if the Mac Pro is searching for OS. Because key board shortcuts don't have any effect I thought perhaps there was an issue with the USB inputs.

AT the end of the day I failed to create anything bootable because I'm not even sure if I am following the correct instructions to insert a DVD that hopefully my Mac Pro will eventually start up from.

If you have another Mac, you use DiskmakerX, a freeware .app that does all the heavy lifting for you. You supply an 8GB or larger USB stick, and a downloaded (but not yet installed) version of MacOS to be placed on the stick. Directions are included on DiskmakerX web site and in the DiskMakerX Application.

The sounds you hear may be caused by the micro-controller in the DVD reader, not by anything the CPU is doing. Put the DVDs away. They are slower, and much more complicated to make and have them turn out correctly (for example, it is really easy to copy the disk image file onto the DVD, rather than making an actual bootable DVD.) A USB stick installer is the way to go, unless you know your USB pathways are not working.

Here you go Using Apple Hardware Test - Apple Support

I found the PRAM battery behind the video card and replaced that but the old one checked out as still working. Still no luck getting this to chime and start normally.

if the power-on light is blinking a pattern, that often says, "not enough WORKING RAM to start up".