Mac Pro 4,1 Freezing after Login

Hello all - longtime lurker, first time posting.

I have an Early 2009 Mac Pro Eight Core that is freezing - no mouse movement at all - after logging in to OS X.

When this first started, I did the usual resetting the SMC and PRAM, re-seating RAM to no avail.

I took a fresh, known good Hard Drive and did a fresh install of Mavericks; same problem.

I was able at one point to load the Apple Hardware test onto a thumbdrive, and it indicated no problems.

Yesterday I received 8GB of RAM from OWC in the mail, put in a new HD, Fresh install of Mavericks. At this point the computer was working normally, so I did the upgrade to Yosemite. I was able to use the computer for a few hours, then Safari crashed and when I tried to reopen it it just bounced on the Dock. I forced a restart, and then it began hanging and restarting itself during the boot process. I booted into the recovery partition and was able to Repair Permissions. This got it booting into OS X but back to the previous hanging within about 30 seconds of the desktop being loaded. It now will turn itself off after sitting frozen for nearly a minute. (It did not do this previously that I am aware, though I may have just been turning it off myself before it had a chance) Sometimes, if I am fast enough I can open the Console but I have not been able to see any Kernel Panic logs.

When booting into Safe Mode the behavior is the same - the system hangs moments after the desktop loads.

There are no error lights on on the Logic Board to indicate CPU failure.

I do not have a spare graphics card that is Mac compatible to test, but I don't think this seems like a graphics card failure symptom? It has the GT120 Card in it. I did re-seat the GPU several times, and even moved which PCIe slot it is installed in.

I guess I am wondering if any of the more knowledgeable here would know the symptoms and could confirm my thought that it is probably the Logic Board, and therefore not worth spending any more time or money on.

Thanks!
Ben

666sheep said:

Three quick tests:
Check if any LED lights on logic board. If not, proceed to next.

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No lights are on.

666sheep said:

Remove OWC RAM. Test without it. If it won't solve the problem, try next.

Click to expand...

I have multiple sets of RAM that I have tried it with. The OWC is brand new, it does the same thing with each set, and various combinations of each.

666sheep said:

Remove the GPU and boot without it.
Wait few minutes. If you'll be able eject DVD tray or hear volume increase/decrease sound (in Yose you'd need to enable it in Sound prefs – it's disabled by default) – it's the GPU.

Click to expand...

Since the system is freezing very soon after it comes on, I may not be able change that setting. I will try that, and definitely the CD tray thing shortly.

666sheep said:

Freezes are usually RAM related, next suspect is HDD, last is GPU. Are you sure of this HDD? Try fsck in single user mode, won't hurt.

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This is the 3rd hard drive I have put in and done fresh installs. It does this across all 3, all having been known good drives in use in other machines before being used.

With every fresh install it'll usually run okay for a little while - maybe an hour or two.

I can try running fsck in single-user mode, but I feel as though I have removed the Drive as a variable.

Thanks for the suggestions! I will report back when I try these.

Okay, I booted without the Video Card installed, waited until it would normally have booted all the way into the OS, and then attempted to open the CD tray/change the volume to hear feedback. When I was about to try those, the machine rebooted itself as it does when it hangs, so I think it can be assumed it froze as usual and that the Video Card can be ruled out as a possibility?

I also booted into Single-User mode and ran fsck. The first time I ran it, it reported that the file system has been changed, and also that it appears to be okay. As usual, I ran fsck a second time, this time it reported only that the volume appeared to be okay. Upon reboot, it froze again, though it did run a little bit longer than previous freezes - still only about 45 seconds or so.

Based on someone on another forum's comment about possible heat problems, I booted it just now while feeling the heat sinks of both CPUs - one of them gets noticeably warm (not hot, but warm) while the other remains cool/room temperature.

666sheep said:

Check northbridge heatsink rivets, they tend to break over time, especially in DP. Bad news is that you'd need to remove heatsinks to do that.

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I think this may be it! I stopped by my house on my lunch break just now, and that northbridge heatsink (even with the CPU heatsink on) wiggles a lot - the visible rivet is very loose.

I've found some threads elsewhere about replacing them - I am familiar with doing CPU replacements so i think I can handle it.

My main concern now I suppose is whether or not the Northbridge is fried or not - would it come on at all if it was?

Quick question - will putting thermal paste on the northbridge be the same process as it is for a cpu when replacing the clips?