My MacBook Pro mid-2012 has been acting up lately. A year ago I replaced the original hard drive with a Samsung SSD 850 EVO 1TB, and everything was fine. Then the SSD got corrupted, and exchanged under warranty. Since I reinstalled the second SSD and installed a brand new copy of the latest Sierra (one 1TB partition on the main SSD), I have been having issues.

The symptoms are:

• Random fails: when I wake it up from sleep or open the lid I find it with the "grey screen with crossed circle" (Similar to this: https://qph.ec.quoracdn.net/main-qimg-b29f58e707cef6f20a882248f4ee558c).
• Fails to find a bootable volume when rebooted (or even shutdown then boot) within a ~20-ish minute timeframe (boots to the folder icon with a question mark, similar to this: https://i.sstatic.net/V5agg.jpg). I have to wait and try to boot it again later. Then it boots as if nothing happened.

What I have done:

• Reset the PRAM. Changes: no significant change in behaviour
• Reset the SMC. Changes: no change in behaviour
• Did the Disk Utility trick where I modify the size of my partition, then set it back to one 1TB partition, in order to have Disk Utility rewrite the partition map (or something). Changes: now it doesn't constantly fails when I close and reopen the lid. Although it may have been the result of the next point.
• Changed the energy settings to default (I have a script I run when I setup a new computer, and it includes some non default power management settings). Changes: see previous point.

Questions:

• Does it seem like a hardware failure or a software failure to you? What I could do to know for sure?
• Any idea how I could reliably fix this?

I have several full backups of my data, so I can try virtually anything. I'm determined to find out how to fix this. Perhaps installing a stock version of Sierra and not change anything at all, and use it like this for a few days could help me figure things out in more details?

Thanks for your help!

My MacBook Pro mid-2012 has been acting up lately. A year ago I replaced the original hard drive with a Samsung SSD 850 EVO 1TB, and everything was fine. Then the SSD became corrupted and was exchanged under warranty. Since installing the second SSD I've installed a fresh copy of the latest macOS Sierra on a single 1TB partition and have been having issues ever since.

The symptoms are:

• Random fails: When I wake it up from sleep or open the lid I find it with the "grey screen with crossed circle" (Similar to this: https://qph.ec.quoracdn.net/main-qimg-b29f58e707cef6f20a882248f4ee558c).
• Fails to find a bootable volume when rebooted (or even after a shutdown and reboot) within a ~20-ish minute timeframe (boots to the folder icon with a question mark, similar to this: https://i.sstatic.net/V5agg.jpg). I have to wait and try to boot it again later. Then it boots as if nothing happened.

What I have done:

• Reset the NVRAM. Result: no significant change in behaviour
• Reset the SMC. Result: no change in behaviour
• Did the Disk Utility trick where I modified the size of my partition, then set it back to a single 1TB partition again, in order to have Disk Utility rewrite the partition map (or something). Result: now it doesn't constantly fails when I close and reopen the lid. Although it may have been the result of the next point.
• Changed the energy settings to default (I have a script I run when I setup a new computer, and it includes some non default power management settings). Result: see previous point.

Questions:

• Does this seem like a hardware failure or a software failure? 
• What can I do to be sure either way?
• Any suggestions on how I can reliably fix this?

I have several full backups of my data, so I can try virtually anything. I'm determined to find out how to fix this. Perhaps installing a stock version of macOS Sierra and not changing anything at all, and using it like this for a few days could help me figure things out in more detail?