I have a very similar condition. On a new pc I finished about a week ago, my mobo (Asus Rampage Formula III) only sees 8gb of the 12 gb of RAM installed (but no other problems). I read that simply resetting the CPU often fixed that problem, so I remove the Corsair cooler installed, reset the CPU, and replaced everything. Now it won't POST at all, no beeps, no CPU LED--although all the fans run fine. After reading your post and some other threads, I wonder if the problem might be between the CPU and the heatsink--I think I maybe was a little too careless about removing the old paste and replacing it evenly. It seems that sometimes makes the CPU refuse to work. Tomorrow I'll try replacing the paste and reasssembling the thing, and let you know if that helped.
For anyone else--if my CPU had been "fried", would that leave visible damage? Because when I checked it again all the contacts looked fine.