Q: HELP. My mac pro has had a kernel attack on startup

If you are getting the progress Bar, it is trying to boot normally. This could happen if your Drive is really, really sick, but is more likely an issue with not holding the keys soon enough.

You could try holding down Option from power on until you get the Startup Manager screen, then selecting the Recovery_HD.

For a wired keyboard, you should hold down Option or Command-R even before you power up. (The timing for a wireless keyboard requires you to wait until the chime is ending.)

If none of this gets you anywhere you will need another drive with a System on it that can boot your Mac Pro 2008 model. The 10.6 Installer/Utilities DVD is such a system, as is any thumb drive Installer/Utilities drive you may have made along the way.

With this much trouble, you should be thinking seriously about a replacement Hard Drive as well.

"Recovery- 10.10.3"

Yes, choose that one!

That is a very small Recovery partition that can boot your Mac with a Minimal OS and give you lightweight access to Disk Utility, Terminal, Resetpassword, ReInstall Mac OS X (from the Internet) and a few others.

Use its Disk Utility and try to repair your disk from there. Run it repeatedly until it comes clean or gets stuck. DO NOT erase your drive -- its recommendation to do so is a holdover from when drives cost $1000, and the prize was your drive. In today's world, drives cost under US$100, and your DATA is the Prize.

Also from there, if it comes to it, you can download and Re-Install Mac OS X on a new drive, skipping older versions and going directly to the last-running version. I strongly recommend you NOT re-Install on a flaky drive, but use a new or repurposed drive and leave your old one intact until you have exhausted all means for getting your files back.

(if you have a Trusted Backup, you are free to do whatever you like.)

Do you have the original Apple RAM? Install the bare minimum into the correct slots, as printed on the side of the access door or in the user replaceable parts manual…

Apple - Support - Manuals

10.10 needs 2GB, but I would go down to about 4GB if you have pairs of DIMMS that can do that.

If you can't get recovery or a normal boot to work from the internal disk you will need to use another disk, either a USB installer for 10.10 or a full OS X installation (e.g. a pre existing bootable backup or a HD from a similar model of Mac).

http://diskmakerx.com/

Create a bootable installer for OS X Mavericks or Yosemite - Apple Support

You an also try Apple Hardware test (or diagnostics on newer models)…

Using Apple Hardware Test - Apple Support

You may need the grey install disks if you have them, one has instructions for the hardware test tool printed on it.

It could indicate an error if you are lucky, run the normal & extended modes several times to be sure. Also consider enabling loop mode (cmd+L) to run indefinitely.

If you have access to another Mac you can also use Target disk mode to do repairs or recover data.

How to use and troubleshoot FireWire target disk mode - Apple Support

Finally verbose mode may spew out enough info to give you a clue what is failing …

Mac OS X: How to start up in single-user or verbose mode - Apple Support

That may just be a longshot, record or photograph the screen if can when messages get stuck.

How did you try AHT?

On the internal HD, on an installer disk, on a USB stick?

There is the option to make a USB AHT installer, this has a nice list of AHT downloads if you can work out the model details…

https://github.com/upekkha/AppleHardwareTest

I made a script to create one of those…

https://gist.github.com/drewreece/2e5eed7dbfbd5dd7e929

RAM should be checked during 'POST' so it should be functional, however it could have errors that occur during use, so it's important to be double check it.

Many Linux distro's have memtest if you want to try another OS to check the memory.

Yes, those cards do go bad.

It does sound like it could be your GPU. Do you have any messages or logs that tie in with your research?

Verbose mode may show useful diagnostics…

Mac OS X: How to start up in single-user or verbose mode - Apple Support

Remove & re seat the graphics card if you haven't already done so.

I can't make much out in the verbose output sorry.

Does your Mac normally have any sharing services enabled? If you can view it on the local network you can see if it is completing a boot. Ideally you have remote access turned on so you can get a ssh connection to it. That could allow you to see if it gets to a state beyond where it fails with the graphics card. Your Mac may not be booting correctly after so many forced shutdowns and having no GPU will prevent screen sharing from working.

If you can read any of that verbose text search around for more info, but it does seem like the symptoms so far are part of a dead/ dying graphics system.

I think the best thing for you to do is to try another graphics card.

There is one experiment you could try.

Let it run until you think it is fully booted up. Then press the control and Eject keys on the keyboard simultaneously. If you could see the screen, this familiar dialog-box would be showing:

any key except these few will cause the System Beep sound:

R will cause it to Restart. S will put it to sleep (and the power light should blink slowly). Esc will cancel. Return will cause a controlled Shutdown.

If the system is crashed or kernel-panicked, you will NOT get System Beep for stray keys.