macbook pro mid 2012 won't start
I've added a comment to your question seeking some clarification on your issue.

However, in the meantime, I'd reset both the NVRAM and SMC again (and in that order) using the steps below. 

Before doing so, ensure you have no external hardware connected and that you're using the built-in keyboard.

Reset the NVRAM

Reset the NVRAM on your particular MBP following these steps:


Shut down your machine. Yes, a full shut down, not just logging out.
Press the power button and then press the commandoptionpr keys. You have to make sure you press these keys before the gray screen appears or it won’t work.
Hold those keys down until your Mac reboots again and you here the startup chime.
Let go of the keys and let your Mac reboot normally.


Note: When you log back in you may need to readjust some of your system preferences (e.g. speaker volume, screen resolution, startup disk selection, time zone information, etc).

Reset the SMC

To reset the SMC on your particular MBP, follow these steps:


Shut down your computer
Keep the power cable plugged in.
Press at the same time shiftoptioncontrol (on the left side of the built-in keyboard) and the power button
Let go
Turn your computer back on with the power button.


After resetting both the NVRAM and SMC, what happens? Does the issue still persist? If so, see if you can test your hardware as follows.

Run Apple Hardware Test

Your model MBP uses Apple Hardware Test. To use this, follow these steps:


Shut down your MacBook Pro 
Restart your MacBook Pro
Press and hold the D key before the gray startup screen appears.
After a while, Apple Hardware Test (AHT) will start.
When prompted, select your language and click the right arrow. 
When the AHT console appears, you can choose to run Basic tests by clicking the Test button. However, I suggest you select the "Perform extended testing" checkbox before you click the Test button.
Your test results will appear in the window in the bottom-right of the console.


Note 1: that the extended test will take some time. Take a note of the results and report back. 

Note 2: If pressing and holding the D key at Step 3 doesn't work, start again at Step 1 and, at Step 3 press and hold both the OptionD keys instead. This will try and run diagnostics from the internet instead, so you will need to allow more time for it to complete.

Let me know if you can actually reset the NVRAM and SMC and test the hardware.