Freezes and screen won't turn on after shutdown

[LiamSp]

Hi,

I'm having a lot of trouble with my iMac Retina early 2015, and I can't figure out what's wrong with it. The problem is if I use the mac for a period of time, sometimes it can be almost a whole day other times it can be a hour. It all of the sudden freezes completely and the only way of getting it to work is to do a hard shutdown (holding the power button until it turns off).

But when I try to turn it on back on the the screen won't turn on. And I have to again do a hard shutdown, sometimes it takes around 5-6 times before the screen turns on. And if the problem occurred once and I try to use the Mac immediately after, it freezes within the first 10 minutes, and the whole procedure has to be repeated for another 10 minutes of usage. The only way to get it to not freeze up is if I don't use it for like a day, but that still only gives me around 3-4 hours before the problem occurs again.

I sent it to a repair shop to get it fixed, I figured that maybe its the hard disk. They ran some Apple test and told me it's not the hardware but the software causing the problem. So they factory restored it and gave it back to me. But it didn't fix the problem.

Any thoughts on what could be the cause of this?

 

[keysofanxiety]

You can download SMART Utility to verify if your HDD's failing.

But in all honesty it sounds like a GPU failure.

 

[LiamSp]

You can download SMART Utility to verify if your HDD's failing.

But in all honesty it sounds like a GPU failure.

Thank you for your answer.
I just downloaded the program you recommended and it said passed on all the disks. How can I check if my GPU is the issue?

 

[keysofanxiety]

Thank you for your answer.
I just downloaded the program you recommended and it said passed on all the disks. How can I check if my GPU is the issue?

You can try download GpuTest and put it under stress. It's not a perfect method of verification, but if the system freezes or exhibits similar issues shortly within the test, this would indicate that the graphics card is on its way out.

Similarly, you can download MemTest and then once installed, open Terminal within OS X. Then type in memtest all 10. Ensure you also have Activity Monitor open at the same time to monitor RAM usage. If it's not using much of the RAM, open another Terminal window and run the same command until it's at ~80/90% usage.

This way, if the system freezes shortly within MemTest, it would indicate an issue with the RAM.

As mentioned earlier, not really a perfect way of troubleshooting for either, but it should elucidate whether it's the RAM or GPU.

 

[LiamSp]

You can try download GpuTest and put it under stress. It's not a perfect method of verification, but if the system freezes or exhibits similar issues shortly within the test, this would indicate that the graphics card is on its way out.

Similarly, you can download MemTest and then once installed, open Terminal within OS X. Then type in memtest all 10. Ensure you also have Activity Monitor open at the same time to monitor RAM usage. If it's not using much of the RAM, open another Terminal window and run the same command until it's at ~80/90% usage.

This way, if the system freezes shortly within MemTest, it would indicate an issue with the RAM.

As mentioned earlier, not really a perfect way of troubleshooting for either, but it should elucidate whether it's the RAM or GPU.

The link you provided for the GpuTest shows a devil saying "Forbidden" and the MemTest is outdated for Capitan and fails to install. I tried to search for other ways but failed to find any. Do you got any other ways I could check this?
And again thank you.

 

[keysofanxiety]

The link you provided for the GpuTest shows a devil saying "Forbidden" and the MemTest is outdated for Capitan and fails to install. I tried to search for other ways but failed to find any. Do you got any other ways I could check this?
And again thank you.

Urgh, I'm just the worst. Didn't check my URLs, sorry.

GpuTest can be found here: http://www.geeks3d.com/dl/showd/391

Can't find MemTest for El Cap I'm afraid. I didn't realise it only goes up to Yosemite.