CPU Upgrade i5 3.4 Ghz to i7 7700k?

I recently opened up my 2017 iMac with the core i5 3.4 GHz CPU to clean it up and put an SSD in it. I also decided to swap the CPU to an i7 7700K while I was in there. Everything went smoothly, but after the CPU swap, the computer wouldn’t boot. I could hear the fan, but nothing else really happened. I put the original CPU back in and everything worked fine. I closed everything up and decided to give up on the idea as I found myself lucky swapping the CPU twice and not breaking anything.

My question is: was the 3.4 GHz CPU upgrade in the first place? The official spec sheet shows all other processor options configurable to i7 except for the 3.4 GHz i5. I assumed it wouldn’t make a difference if the original CPU was a 3.4 GHz or a 3.5 GHz. I also bought the replacement processor secondhand so there’s always a chance of that being a bad one. I don’t think I’m ever gonna open the iMac again. I’d just like to know if the lowest spec CPU was the issue.

Thanks!