Chosen Solution
I put two 8GB DDR 3 1333 MH ram in my mac mini Mid 2011. It booted fine and the RAM showed up on the “About this mac” window indicating that it was OK, but after a short time it froze and the monitor had coloured lines running horizontal. Tried it with an 8 GB chip and a 4GB chip. It work okay for half an hour then went ape sh#t again. The monitor is an Apple cinema display used with the Apple adapter.
It sounds like you damaged something on the logic board in the process. Did you encounter any difficulties taking the logic board out? Did you use a ESD wrist strap & mat? Unlike desktops & laptops you need to fully remove the logic board.
