I just received a new i5-9600k, which I bought to replace my i5-6600k. Unfortunately, after installing, the system appears to fail the POST.
I am installing to a MSI Z170A SLI board, and using an h100i v2 along with 2 sticks of ram, installed in their proper slots. The system does still boot fine once I reinstall the 6600k.
My current suspicions are first an issue with the socket (I'll elaborate shortly), with the Mobo bios, or perhaps with the chip itself.
As I was installing the new chip, I saw that there was a small amount of thermal paste along the edge of the socket. I've cleaned it as well as I could so far, but it has been impossible to get most of it out without bending the pins. After this process, I triple checked for bent pins, and didn't find any. Also, the paste I am using is corsair brand zinc oxide paste (no, not arctic silver paste. Sue me). I'm not sure if the pin configurations are different enough that the 6600k might run fine while the 9600k could be blocked by a small amount of the paste.
I'm out the apartment right now, and posting from my phone, but I can later attach pictures or maybe even a short video of the system failing to boot, if that would be helpful in helping me troubleshoot this.