according to Apple) these models only support 8GB of RAM. This model has two memory slots capable of taking 204-pin PC3-12800 (1600 MHz) DDR3 SO-DIMM memory chips. Solved! Macbook Pro 2012 Late Retina i5 Screen ReplacementYour question doesn't specify which model of MacBook Pro (Mid 2012) you're asking about and the answer may be different depending on model. Solved! How I fixed my Macbook with water damage

Solved! New 16' MacBook Pro M1X and Bootcamp. Question Pending item to be downloaded on iTunes (Macbook Air mid 2019) Question How to Install Old Version of OS X in VM to run Flash 7 on 2020 MacBook Pro Question Late Delivery Time (non M model) for 16' MacBook pro. Question MacBook Pro A1502 model + Lost MacOS (no recovery partitions) and cannot boot MacOS USB drive! Question Big Sur on unsupported MacBook Pro? Question In the long run, which Macbook would perform consistently? Question Macbook Pro mid-2014 starts flickering then shut down randomly !! Question 2015 13' MacBook Pro Kernel Panics when waking from sleep Question MacBook Air M1 with HP Thunderbolt Dock G2 Question what to do with a 2006 Intel cpu MacBook Pro? Question MacBook A1181 stuck at progress bar then turns off Again none of the Macbooks can be upgraded later so build to order to your expected needs for the next five or six years. Start thinking about getting a new laptop. Buy the same model fully functioning off eBay used. You may even get a few bucks selling your old motherboard for parts or repair only on eBay. Then follow an iFixit guide for your model to replace the motherboard yourself. Buy a used motherboard for your model off eBay from a reputable seller. Just be aware you cannot upgrade the newer models. The cost difference between what you get for it and what a used MBP 2013/2014 go for is likely less than a motherboard replacement at a shop. Just be sure to sell for parts or repair not used on eBay. It's so old I wouldn't expect too much for it. Sell it and get a newer used MacBook Pro. You can just live with it having 1x8GB. You'll just waste money having it diagnosed.

Which would be ridiculously expensive (especially through Apple) for a computer that old. The only repair would be replacing the motherboard. Just to be sure (make sure it is properly seated). Try just the one RAM module you know works in the other slot.

Macbook pro 13 mid 2012 ram ssd