Can't connect to Pi4 4GB

I am not able to get my new Pi4 (4GB) to update.
I’m using the Pi4 32 bit image on a 32GB microSD card.
After powering up the yellow LED on the Ethernet jack turns on. Within 10 seconds the green LED (Ethernet jack) starts to flicker. Within a few seconds the yellow LED turns off (never to turn back on).
I’ve left it on overnight with no luck. I currently have a Pi3 running the latest HA with no issues.
My buddy offered to try it at his home and had success using my micro SD card and hardware (Pi4, power supply and Ethernet cable. My router is the ASUS RT-AC88U. I have never had any issues in the past with this high-end router. I have a 10/100 NETGEAR switch in between so not connected to gigabit connection. I also tried plugging in directly into one of the 8 gigabit ports on the router with the same outcome. Any ideas would be greatly appreciated.

Can you ping the Pi4 when its connected?

Does it show up in your router as a connected device?

Can you connect a monitor and see where the output has stopped?

Are you trying hassio.local or trying to access via IP? (e.g. http://192.168.1.2:8123) The latter is preferred as not all routers support mdns and sometimes it can just be flakey.

It shows up in the connected device list (my router) after my buddy went through the HA updating process. I have not tried to ping it yet nor have I connected it to a monitor. I have tried to connect with the ip address with no luck. I’ll try these two things this evening and report back.

Looks like this is the problem. This all happened after I updated HA the other day. I have AsusWRT in my config.
Both my Pi3 and Pi4 were both knocked out of service. Now I have to borrow a different mfg. router to try to correct this problem and wait until this is fixed.