Late 2012 iMac won't turn on after RAM upgrade

[paardenkapper]

Feels like everything I touch turns to crap lately.

My fiancees iMac from 2012 had only 8 GB of RAM, so I bought 2 inexpensive sticks of 8 GB, opened the thing and dug out the mainboard.
After putting everything together and pressing the power button nothing happened. What I can see:

1. The CPU fan spins up very briefly and then stops
2. The lower of the 4 LEDs is green and stays green all times

Inserting the power cord with the power button pressed makes the fan spin up but that's it.
I cannot reset the PRAM, because it will not even boot to that point.

Is the RAM faulty? In my experience I'd at least get some sort of beeping, right?

 

[TwoH]

Hey, don’t feel too bad about the machine not turning on - iMacs can sometimes be a little picky and weird about when they want to accept ram.

By how you’ve worded it I’m assuming this is a 21.5” machine. My first instinct on this is there being an issue with the ram - the indicators aren’t pointing towards anything else.

Your best bet may be to reseat the ram and see if that has any fix. If it is a 21.5” and your fingers are nimble enough - you are able to reseat/change the ram only by taking the fan out of the machine.

So try a ram reseat. If nothing has changed, try putting the original ram sticks in and seeing what you get.

 

[paardenkapper]

Thank you. After reseating the memory quite a few times I remembered one thing.
When I had the motherboard on my desk I repasted CPU and GPU and must have reseated the CPU shoddily.

Did it again making sure the CPU sits like it should - boots up with 16 gigs like nothing ever happened.