New PC Build - POST issue

Apologies in advance for the essay.

Just finished building my first PC. Watched tons of videos, checked 3 different part compatibility checkers, been planning and slowly acquiring parts for months. Complete the build, go to power on, no display. All my RGBs work on case fans, cooler fan, RAM, GPU.  Power button on my case blinks white rapidly for a bit, then on/off about every second for a bit, then 3 seconds on/3 seconds off until I power it down. No display at any point. My motherboard has no status LED, and no speaker.

I tried running HDMI from my GPU to TV, then disconnecting my GPU and running HDMI from my motherboard to TV, still no display. Even pulled the rig upstairs to a different TV. Still no display, still same power button blinking pattern.

I took my cooler off the CPU, checked the chip, it all looks okay. No debris in pins, no excess thermal paste.  CPU arrow oriented correctly. RAM is securely clicked into the correct DIMM slots per motherboard manual. GPU is/was connected and powered by 2 PCIe connections from my PSU. All the necessary PSU and case connections have been made. 24 pin motherboard power, 8 pin CPU power, the USB connections from the case, etc. all connected.

Any ideas on what might be going on? Any troubleshooting support would be greatly appreciated.  Specs below:

CPU: Intel i7 12700KF

Motherboard: ASUS Z690-P Prime WiFi w/ DDR5 

RAM: Corsair Vengeance DDR5 2x16

GPU: Gigabyte NVIDIA GeForce RTX 3080


Case: Lian Li LanCool III w/ RGB 

PSU: Corsair CX750 

CPU Cooler: ThermalTake CX200 SE

Display: Samsung 65" 4k UHD TV


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