if 3 of the 4 work and you can use each one at a time in slot 1 then the 4th slot is physically bad.
I have switched the cards around into all the slots to test. All of the slots work, as well as all of the cards.
I'm not certain if it was just luck or what but I had zero issues upgrading my machine today. After reading this thread, I was concerned that I'd have issues.
Today I installed (4) 16GB Corsair 3200 sticks, turned on the machine, waited for about 3 minutes before BIOS kicked in, and shazam, all good.
The BIOS automatically picked up all of the RAM, recognized the 3200 speed, enabled XMP, and set the voltage to 1.35. I literally did nothing but insert the sticks and turn the machine on.
I've just posted a message about the newest BIOS stopping my 3200 64GB RAM working. It worked perfectly up to that point. Does your PC have BIOS 1.0.7?