Mac boot problems

[Kwack636]

Hi guys, new member here and also new to iMacs.
I’ve recently bought a 2011 iMac 27” off a friend, I purchased it for a decent price knowing it had a problem. The problem is in the boot, it starts to load then crashes with a grey screen. Sometimes it lets me log in to my account then freezes and goes off again. It’s recently had a new motherboard fitted so I’m hopeful to rule that out. I’ve noticed the HDD stoops ‘ticking’ just before the freeze. Could this be a HDD problem or possibly the GPU? Thanks in advance. I have tried looking for the problem.
Martin

 

[hobowankenobi]

Could be several things.

First to rule out would be hard drive and/or OS.

Several ways to do this, but the easiest may be to round up an external hard drive, and wipe it, and install a fresh OS on it. Booting to the external would be a good test to rule out the existing OS, hard drive, along with the SATA bus/cables.

Once you have the drive, you can boot into internet recovery model to grab a new OS...or if you have access to a similar Mac you could download the MacOS installer on it too.

A 2011 Mac can probably run 10.13, depending model.

 

[Fishrrman]

Probably a bad GPU.
The 2011 product line had terrible GPU's...

 

[Kwack636]

Could be several things.

First to rule out would be hard drive and/or OS.

Several ways to do this, but the easiest may be to round up an external hard drive, and wipe it, and install a fresh OS on it. Booting to the external would be a good test to rule out the existing OS, hard drive, along with the SATA bus/cables.

Once you have the drive, you can boot into internet recovery model to grab a new OS...or if you have access to a similar Mac you could download the MacOS installer on it too.

A 2011 Mac can probably run 10.13, depending model.

Thanks for the reply. I’m kind of hoping it’s the HDD, I have a. sata windows HDD that will work for this but is formatted to fat32. Is it possible to format it so I can use it with the Mac?

 

[Kwack636]

Probably a bad GPU.
The 2011 product line had terrible GPU's...

So I believe, I’m really hoping it isn’t

 

[hobowankenobi]

Thanks for the reply. I’m kind of hoping it’s the HDD, I have a. sata windows HDD that will work for this but is formatted to fat32. Is it possible to format it so I can use it with the Mac?

Yep. Nearly any SATA drive will work, but needs to be formatted HFS+ on a Mac to be able to install and boot the OS. I would suggest an external drive first, to test.

As has been pointed out, there are other known hardware issues possible....no sense in opening the machines and swapping drives until you have more proof that is the issue.

 

[Kwack636]

Yep. Nearly any SATA drive will work, but needs to be formatted HFS+ on a Mac to be able to install and boot the OS. I would suggest an external drive first, to test.

As has been pointed out, there are other known hardware issues possible....no sense in opening the machines and swapping drives until you have more proof that is the issue.

Thanks again for the reply. I’m looking at possibly replacing the gpu. Is it just the Radeon 6970 that will go in this model? Or will another go in it?

 

[hobowankenobi]

Not sure off hand if the GPU is repacable. On some iMacs, it is soldered on...so the entire logic board would have to be swappted. Some models do have a replacable GPU. Do you know the exact model number to verify? Would be something like: iMac12,1