Swapped cases for a friend's PC and it is now not posting. I've tried all the troubleshooting steps I could do and scoured the internet for a solution but none has worked. 
 
It turns on, but doesn't post. While swapping cases I repasted the cpu/cooler (didn't remove cpu). I am getting the code "4C" on the debug screen tho. According to the instruction manual, this is a CPU issue. But all I did was change the paste, I didn't even remove the cpu,  so it can't be bent pins (right?...).
The LED error lights for the memory and the pE4 and PE2 (This is the PCIE slot that the GPU is in) slots are also on. And interesting enough, even tho the debug code is 4C, the CPU debug light isn't on.
I also did test the GPU, PSU, and RAM on a test rig and the test rig was able to boot up with no problem. The only component that I'm not able to test is the CPU since my test rig is an AM4 board. 
The PC did work about a month ago, but was not touched until I swapped it into a different case.
 
Things I've tried:
Changing from BIOS1 to BIOS2
Booting with only 1 ram stick, and in different slots. Also tried different sticks of ram
Tried a different PSU
Resat all cables and GPU
Double checked for any breaks in the wiring and made sure everything was properly seated
Removed CMOS battery for 10 minutes
 
 
Specs:
Board: EVGA Z370 Classified K
CPU: i5-8600K
GPU: ASUS ROG 1070TI
RAM: Corsair Vengence Pro RGB 2x8
PSU: EVGA Supernova G3 Supernova 750W 
Storage: Samsung 980 m.2
 
Any help is appreciated. About to just buy a new board lol. If that doesn't work, then new CPU as well. Thank you!

Correct, I did not test it right before swapping the case. Which I suppose does sound stupid now… My friend did say it was working fine last month, so I did assume it would be fine. This is just a secondary pc he had so he doesn’t really use it.

I checked the cords many MANY times. Probably more than I should’ve (I probably wasted A LOT of time doing this LOL). Every time I touched the pc, I triple checked that all the cables were correct and seated properly.
They are the OEM cables.
There is no beeping coming from the board.
I had nothing plugged into the pc except for an hdmi cable (in the gpu, not the motherboard)
Motherboard screws are good
I tightened/loosened the cpu cooler in an X pattern, in a series of small steps.
I/O shield is good.

I guess the only thing left to try is to boot the board out of the case and check for possible shorts. I really didn’t want to do this because at the end of it all, I was so over it. I was there for hours swapping things out and quintuple checking everything after each step. Taking it all out was the last thing I wanted to do LOL.
I will try it and report back. Thank you for the suggestions

Only 2 others things come to mind; 1) Any chance a board mounting post was not removed if the board pattern is different than the original? 2) Could the thermal paste be a sliver compound and got on the pins?