Mid 2012 Macbook Pro doesn't progress beyond apple logo and progress bar. Also resolution is low on startup screen. Sometimes screen goes blank.

Use your working laptop and install macOS to the new SSD while it is connected externally. Test boot the new SSD externally on your working laptop to verify everything is Ok. You could in theory remove your own drive and connect it externally to the non-working laptop and attempt to boot the non-working laptop with your drive connected externally, but this may pose some risk to your drive if the non-working laptop is damaged which is why I suggested doing this with the new SSD instead.

If the non-working laptop is able to boot a full macOS drive externally, then you can install the drive internally to see what happens. If the drive does not work when installed internally, then maybe the internal hard drive SATA Cable is loose or bad...if using the new SSD, then perhaps the new SSD is not compatible with this laptop when used internally.

You can connect the new SSD externally using a USB to SATA Adapter, drive dock, or enclosure.

You can create and use a macOS USB installer in order to install macOS....if the non-working laptop never had macOS 10.11 or 10.13 installed, then you may instead need to use one these operating systems instead of a later OS until the system firmware of the non-working laptop is updated.

Create a bootable installer for macOS - Apple Support

CyberSam65 wrote:

I have been troubleshooting this Macbook Pro. It looks to be a Macbook Pro 15" Mid 2012. I have the same model. I have upgraded the internal drive with an SSD running Mac OS 10.10 Yosemite.

I have purposely gone back to the OS it had on it originally. The only thing it seems to be able to do is show the bootable USB and the internal SSD when the Option key is pressed down.

I have done everything humanly possible to this machine except upgrade the battery which is dead and has to be run off the power. It won't boot into recovery mode, or safe mode - gives a Blue screen of death mac style. I have reset the SMC.

When I found this laptop it did have mould on it and maybe there was moisture inside. Sometimes the screen goes blank.

I know the drive is working because I created it on my Macbook Pro Mid 2012 and it booted from the drive.

Sam

A found Mac...(?)

Apple Recycling Programs

Apple Free Recycling

If your Mac starts up to an Apple logo or progress bar

If your Mac starts up to an Apple logo or progress bar - Apple Support

If your Mac doesn't start up all the way

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