Can't login admin user in MPB 2012

[Romahaaa]

Weird thing happened just recently on my old MBP.
From the beginning (may be this give some important info)

1. I have replaced the HDD to SSD ~4 months ago and installed Mojave
2. Laptop was used sometimes, never had problems with it
3. Last 3 months wasn't used at all. It was switched OFF.
4. 2 days ago turned it ON and by some reason 1st and 2nd password access was denied. Password input was correct 100% as it's very simple num pin. on 3rd attempt it was accepted.
5. Yesterday tried to use it again (laptop was in a sleep mode) but now I can't login at all. Same password never being accepted.

I tried to reset password using AppleID (was changed successfully but password is still not accepted on login).
Tried to boot on Single User Mode, Recovery Mode, Reset SMC, NVRAM, but it looks like laptop doesn't react to any input at all. I always see Apple Logo on gray background first and after Login screen on the same gray background with options to turn off or restart...

First time I met such a problem. Googling doesn't help at all as all the recommendation are about reseting the password, what is useless.

What can I do here?

 

[Romahaaa]

Important note to add - when I tried to input password yesterday there was kind of glitch - the keyboard input some symbol without any button being pushed.
I also tried today an external keyboard (just in case there is some input issue, but the problem still existed.

 

[Fishrrman]

When you changed the HDD to SSD, did you also change the ribbon cable that connects the drive to the motherboard?

These can be a point of failure in the 2012 design Unibody MacBook Pro.
When the cable "gets flaky", proper communication between the drive and the motherboard becomes spotty, and to the user it can look like drive or motherboard "failure", but in reality it's "just the cable".

You can get the part number from ifixit.com.
Buy the cable from them, or elsewhere online.
Since you already have changed out the drive, you know how to "get inside".

Here's a way to "test the issue":
Boot from your OLD drive, using USB3.
Put the old drive into an enclosure or perhaps a USB3/SATA docking station.
If the computer boots right up using an external boot drive, that would point towards the ribbon cable as the "offending part"...

 

[Romahaaa]

Here's a way to "test the issue":
Boot from your OLD drive, using USB3.
Put the old drive into an enclosure or perhaps a USB3/SATA docking station.
If the computer boots right up using an external boot drive, that would point towards the ribbon cable as the "offending part"...

Just tried, but seems mac doesn't recognize any external device at all, loading directly to it's internal macos with the same login screen.
Same behaviour was when I tried to start with recovery USB disk...

I can try to open the Mac and disconnect internal drive at all, leaving only external old HDD

 

[Romahaaa]

So, I did some progress.
1. I removed SSD leaving mac without hard disk at all
2. Tried to boot old HDD with MacOS installed on it by USB - no success, mac didn't recognize it.
3. Tried to boot Recovery Disk by USB - that worked.
4. Tried to load SSD by USB - login password accepted the system loaded.

So, seems @Fishrrman your suggestion was correct. Will buy a new connector and replace it. Will report here about the result.

Thanks a lot!

 

[Fishrrman]

Let us know if the new ribbon cable works for you...

 

[Romahaaa]

Well, I have changed the ribbon cable and now Mac works again - logging in without any issues and performance increased a lot.
But... I still see the problem I met 1st time when tried to login before cable replacement - mac inputs to the password field a looot of symbols, same if you would hold any keyboard key for a long.

Now, after cable replacement, that happened couple of times as well. Furthermore, more often it was like "fn" buttons was "pushed". For example, not pushing any additional key, but only any letter it would input some alternative symbol, set to that key like "ß", "¬", etc (on my MBP 2015 I cant type it using "alt" key, but on MBP 2012 only using "fn"). If I hold "fn" and type same key it inputs me a normal letter...

We leave in high humidity climate, so I just guess, maybe it's a keyboard or it's connector issue? Is there any way to diagnose it?

 

[Romahaaa]

@Fishrrman some kind of problem here again...
After writing the post above I turned on the mac today, and absolutely the same behaviour appeared - login password doesn't fit, safe mode not loaded, etc.. everything what I described in the 1st message.

.... Any guess?

 

[Fishrrman]

"We leave in high humidity climate, so I just guess, maybe it's a keyboard or it's connector issue? Is there any way to diagnose it?"

That could actually be the problem...

 

[Romahaaa]

Some update.
I just guessed, what if password couldn't be accepted cause the actual input was inverted, same if to type it with "fn" pressed. And I was correct. So, seems that was the main problem, not ribbon cable.
But... before changing cable I tried to attach external keyboard, and the result was the same... looks like it's not the integrated mac keyboard issue, but something else... I have no clue what can it be