I got my late 2012 27" iMac with 8GB RAM. I purchased 16GB of the recommended Crucial RAM (using the Crucial configurator). After installing the RAM with the Apple RAM, 24GB appeared in system information. However, after shutting down and restarting from a cold boot, it only reported 16GB. After playing around with the slots a bit, I could get it to recognize any 2 RAM chips, but never all 4. So I figured the brands weren't getting along. Ordered 16GB more of the Crucial RAM and same thing is happening. It won't recognize more than 2 RAM chips. The weird thing is that it is not isolated to one slot. Each slot seems capable of recognizing the RAM, but once more than 2 are populated, only 2 are recognized and the other 2 are reporting empty. I have repeatedly tried to make sure they are seated right, and am now running out of ideas other than I may have a hardware issue. The only thing that is keeping me very slightly optimistic is that each port seems to be functional, just not all at the same time. Maybe I'm doing something wrong. ANY HELP WOULD BE GREATLY APPRECIATED. The Crucial RAM is model # CT2C8G3S160BM The iMac is a 3.4 GHz i7.