Mid-2012 MacBook Pro Startup Failure

There are a lot of possibilities here.

What does the power/sleep LED do? Is it solid, or blinking? Is it blinking any codes?

If you press the button on the side of the laptop to activate the Battery Indicator LED, how many LEDs light up?

Try an SMC Reset and a PRAM Reset (hold the PRAM Reset for at least three chimes).

Try running the Apple Diagnostics to see if any hardware issues are detected. Unfortunately many of these 2012 Macs are no longer able to boot to the diagnostics due to a firmware update which introduced a compatibility issue with the online diagnostic's bootloader located on a remote Apple server. The error is something like: "Cannot load EFI/Drivers/TestSupport.efi". It doesn't hurt to try though.

What appears on the screen when you try to boot to the internal drive?

Try an Option Boot by holding down the Option key immediately after the startup chime. Are any boot volumes shown on the Apple boot picker menu (if so what are they)?

You mentioned this laptop may have Linux installed....Are you familiar with Linux? If so, then try creating & booting a Knoppix USB stick. This can be an easy way of checking the hardware is working. Give Knoppix lots of time to boot since the Mac may appear frozen on the Apple boot picker menu while Knoppix boots due to firmware issues/behavior. If you can do this, then I can provide instructions for checking the health of the internal drive.

Another option would be to install macOS to an external drive, but this can be tricky. You can try booting into Internet Recovery Mode (Command + Option + R) to attempt to access the online macOS installer. If macOS is currently installed on the internal drive, then you may be able to run Disk Utility First Aid on it and try other tips in the following Apple article:

If your Mac doesn't start up all the way - Apple Support

Of course if Linux is installed on the internal drive, then you would need to follow Linux troubleshooting methods if you want to try to salvage the Linux installation.

There is a possibility the internal drive or even the internal hard drive SATA Cable is bad. The internal SATA Cable has an extremely high rate of failure on the MBPro 13" (mid-2012) non-Retina model.

You do need to confirm if the built-in Display is working, that the laptop has actually powered on (may not be booting which is a separate thing), or if the laptop is attempting to boot into some type of OS even if it is unsuccessful. A power on issue is different than a booting issue. It sounds like you it is powering on if the power/sleep LED is on. Then we need to know whether the display is working....an Option Boot can easily give you that information since something should appear on screen when holding the Option key immediately after the startup chime.

machelp_apple wrote:

I never heard of Knoppix, but I do have over 18 months of linux experience. I'll definitely give that a try!

You can also use your Kubuntu USB installer as well. I believe the Kubuntu installer will show video on the screen much sooner than Knoppix will. The Kubuntu USB installer also has a "Live" mode option where it will boot to the Kubuntu desktop from the USB stick (it will perform very slowly, but at least you can test basic functionality).

I don't think I should take apart the computer because it might void the warranty if there is any from 12 years ago.

There is no warranty to worry about. Removing the Bottom Case (a Phillips #00, or possibly #0) to check whether you notice any liquid residue and/or corrosion on the inside of the case or the visible side of the Logic Board.

Now I have a different MacBook Pro Early-2015 with keyboard and trackpad failure, but I'd rather focus on the current topic and I will submit another discussion request for the other one.

When both the built-in Keyboard & Trackpad fail at the same time on a MBPro 2015 model, it is due to a bad Trackpad IPD Flex Cable since it has an extremely high rate of failure.

I believe the Mid-2012 one specifically has Kubuntu on it, KDE Plasma 5.27. I might have to submit a support issue to them, and see what they think the issue is.

They probably won't be able to help you since it appears you have a hardware issue of some sort.

Almost forgot.. The internal display will not do anything.

Through out this whole conversation you have never mentioned seeing anything on the built-in Display. If the built-in Display doesn't show anything at all, then either the Display Assembly is bad, or the Logic Board has failed. If you have the 15" model, then there is a chance it may have a GPU failure.

Does the display light up with a white screen (IIRC the non-Retina model had a white/gray screen once powered on)?

If you hold the Option key down immediately after hearing the startup chime, do you see the Apple boot picker menu? If the screen is dark, then shine a flashlight or bright light through the Apple on the back of the display to see if you can notice any icons near the center of the screen since something should be there if it has a video signal even if the backlight is out. It may be easiest to do this in a dark room as well since it is not easy to see the faint video on screen if the backlight is not working.

Are you even hearing the startup chime....you should hear it when performing the PRAM Reset as long as you keep holding the PRAM Reset for at least a minute. If you don't hear any startup chime while doing this, then try using an external wired USB keyboard just to make sure that you don't have a bad keyboard. If you don't hear a startup chime, then either you have bad speakers or a bad Logic Board.

I think there might be a disc inside, but I tried the EJECT button on the DVD drive and it did not eject. Yes, I did the Power/EJECT command and it didn't eject. SuperDrive did not make a noise when it booted up.

While it could possibly affect being able to boot the laptop, it won't prevent video on the display. You would either see a blinking folder with a question mark, or when holding the Option key you would see the Apple boot picker menu screen even if no bootable volumes are found.

I have a Thunderbolt to HDMI cable, so I might hook it up to my television. I had another for USB to VGA, then I realized that cable was for Windows PC..

Getting video to an external display can be tricky on a Mac and a TV may be a bit more difficult. Theoretically you should get some sort of video signal on the external display. If you see video, but not the Login screen, then you may need to press Command + F1 to enable screen mirroring so that the login screen shows up on the external, but sometimes I have found this is not possible until after logging in.

The Apple 85W charger is not going to hurt the laptop. We use them all the time.

Disconnect the battery and try powering on the laptop using just the power adapter. Sometimes a bad battery can prevent the laptop from even powering on. This is very easy to do on a 2012 laptop (especially the non-Retina model since you only need a #0 or #00 Phillips to remove the bottom case although to actually remove the battery (not necessary for testing) requires a Tri-lobe screwdriver. A Retina model requires a Pentalobe 5 driver to remove the bottom case.

Make sure to disconnect the Power Adapter while removing the Bottom Case & disconnecting the battery. Reconnect the power adapter only to see if the laptop will power on correctly & boot to some mode.

If even this does not work to get some type of boot mode, then there is most likely an issue with the Logic Board which would not be worth repairing.

<< there is no startup chime. >>

Then your Mac did not exit the power-on self test successfully. Whether it even started the test us unknowable.

This has NOTHING to do with drives or peripherals, Boot loaders, or Operating systems. The power on self test concerns itself with really fundamental stuff like the processor, and later, the RAM. RAM failures will produce a blinking pattern. You are not even getting that far.

Does the power-on indicator (if so equipped) blink a pattern? if so, how many blinks?

The initial "chime" sound is generated in software when your Mac passes the Power-On Self Test. If the chime occurs and/or startup continues, your Mac is working. The screen should light up and draw a blank gray screen.  Then on to the Disk Drive.

This uses ROM-resident startup software, and will occur even if your Mac uses an alternate boot loader to load a different operating system than MacOS.