Question 2007 iMac freezes while booting

[topfive]

Hello, everyone. This is my first post, so go easy on me. I'll try to describe the situation as thoroughly as possible in this first post.

I have a 2007 iMac 24" that recently stopped booting. There were no apparent performance issues leading up to this; one day it just refused to boot.

Upon startup, I get the typical startup tone, then a gray screen with an Apple logo and a progress bar. When the bar reaches about 55% of the way, it stops. After a minute or two, the screen goes dark for a second, then goes completely gray with nothing on it. It remains like that regardless of how long I leave it.

I'm very knowledgeable about Windows systems, but pretty green regarding Macs (the dead iMac belongs to my girlfriend). I know my way around hardware and am comfortable opening up a computer and replacing defective parts. On this particular iMac I replaced the defective hard disk with an SSD a couple of years ago and it worked fine afterward.

Regarding this boot issue, I have researched the problem and tried the following, none of which solved or affected the boot process:

1. Disconnected all peripherals except keyboard and mouse and rebooted.
2. Booted in recovery mode and repaired the hard disk. No issues found,.
3. Booted in recovery mode and restored from Time Machine. Tried this with several backup points, even going back to the oldest available backup.
4. Booted in single user mode (command-S) and ran fsck -fy to check the file system. Ran it twice, then rebooted.
5. Reset the PRAM/NVRAM.
6. Unplugged the power cable for a few minutes, then reconnected.
7. Booted in verbose mode. The last thing appearing on the console before the gray screen came up was: "Yukon RxRingSize"

Other things I've tried which failed in a different manner:

1. Attempted to boot from the install discs to run Apple Hardware Tests, but that fails. After inserting the disc, I eventually get a garbled screen that is unreadable.
2. My last resort: I booted in recovery mode, erased and reformatted the hard disc (without issue), then reinstalled the OS. Upon booting, the progress bar moves farther (75% or so) before stopping, then freezes in the same manner.

Important note: The systems boots perfectly in safe mode. I can use the computer like this, albeit with the safe mode limitations.

My best guess tells me this is a kernel problem caused by a hardware issue, but I'm stumped as to how to determine which part may have gone bad.

Any help would be greatly appreciated.

System specs:
CPU: 2.8 GHz Intel Core 2 Duo
Current OS: OS X El Capitan, version 10.11.6 (restored via Time Machine)
RAM: 4 GB 667 MHz DDR2 SDRAM
Video: ATI Radeon HD 2600 Pro 256 MB
Crucial 250GB SSD (124GB available)
Boot ROM version: M71.007A.B03
SMC version: 1.21f4
Power On Self-Test Results: Passed (this morning)

That's everything I can think of that's pertinent.

I understand the system is 12 years old. My girlfriend has already purchased a replacement. I just don't want to toss the old one until I've tried everything I can possible do to get it running again. With that in mind, I'll accept any suggestions whatsoever. I'm at a dead end right now with this thing.

Thanks in advance!
Chris

 

[spinningstill]

Do a back up via TM or CCC if you can.

As you may know, SafeMode means no third-party software is running. While in SafeMode, looks for Apps that you know you don't need. There may be an uninstall feature or just put in trash. While in the finder see "go" and hold the option key, next select "library." Scroll down to launch agents see what is there, delete anything that looks questionable. You can also delete Cashes.

Something may have gotten inadvertently installed. Old Adobe can cause issues. Also check for too many users. Delete any you know you don't need (back up first).

Sounds like the machine is still functional, maybe peak out the RAM once all is done and you should have a good functioning Mac. For aftermarket parts, I recommend OWC.

 

[topfive]

Do a back up via TM or CCC if you can.

As you may know, SafeMode means no third-party software is running. While in SafeMode, looks for Apps that you know you don't need. There may be an uninstall feature or just put in trash. While in the finder see "go" and hold the option key, next select "library." Scroll down to launch agents see what is there, delete anything that looks questionable. You can also delete Cashes.

Something may have gotten inadvertently installed. Old Adobe can cause issues. Also check for too many users. Delete any you know you don't need (back up first).

Sounds like the machine is still functional, maybe peak out the RAM once all is done and you should have a good functioning Mac. For aftermarket parts, I recommend OWC.

Thanks for taking the time to reply. I'm pretty sure that the problem isn't related to third-party software, because I when I use recovery mode to reinstall the OS, the install process works fine but upon reboot it still fails in exactly the same way.

That's what makes me think I've got some kind of hardware failure.

 

[spinningstill]

Would check RAM (install new or uninstall and reseat old) and try internet utility. Also, try starting with no peripherals, just use power button.

Here are some more steps:
https://www.lifewire.com/fix-mac-that-stall-on-gray-screen-at-startup-2260831

Grace and peace.

 

[topfive]

Posting my solution in case others might benefit...

I did a lot of researching online regarding this issue, and eventually stumbled on a YouTube video that helped me resolve it. Basically, after a period of time the contacts between the graphics CPU and the video card start to weaken. This can be reversed by removing the graphics card from the iMac and baking it in a 390-degree oven for 8-10 minutes (yes, seriously). That softens the solder enough for the CPU chip to sink down into it and redo the contact points. So many people commented to that video saying that the process worked, so I gave it a try and now I have a perfectly functioning iMac again.

One little note: After baking the graphics card and reinstalling it into the iMac, I booted to a black screen with no video at all. I could could still hear the chime and the hard disk whirring, but the screen was completely black. Some more Googling led me to someone who had replaced his graphics card only to have the same problem about the black screen. He resolved it by opening the box back up and re-seating the graphics card. It turns out that the card can look like it's properly seated, but you actually have to push it in pretty firmly, enough so that you can barely even see the gold contacts on the card. I re-seated mine and it booted up perfectly with no issues at all.

 

[spinningstill]

I had taken my MBP (09, 11?) to an awesome guy in Denver to fix it (graphics issue). He did mention the method you describe and it works for some. However, due to the complications that could occur, it wasn't a method recommended. So, I bought a new refurb and sold the old MBP as is. As an FYI, Apple supports hardware for seven (7) years.