27" Display not working after HDD replacement

I have a 2019 iMac 27" Retina display. It stoped working because of hard drive issues. I use it for video editing and coding, I had considered replacing it, but I didn't want to get a smaller screen or shell out for the studio display and a 1TB Mac mini.

I figured I would replace the drive with a 6TB WD Blue, as the 1TB drive was almost full and I already had an external drive filling up. I ordered the tempeture sensor and followed all instructions carefully. This far from my first repair though it is the first time opening up an iMac.

The replacement went smoothly but I wanted to verify everything worked before I sealed it back up. So I booted from the internet and tried to find the new drive with no success. Stumped, I decided to re-install the old drive to see if I could figure it out.

At this point the display stopped turning on. I would hear the startup sound but the screen never turns on. I tried multiple times, and have switched back to the 6TB. I have tried connecting the external monitor I have been using with this iMac. Nothing appears to work. I have decided to give a rest for the evening but I really would like to be able to use it next week.

Can I trouble shoot and fix this or is this just broken beyond reasonable repair.