Display Issues after PSU replacement

Hello everyone,

This is my first post to an Apple forum but I'm experienced computer technician.

I recently replaced the power supply unit on a family member's iMac. Prior to the replacement, There was no response from the iMac and with the power cable plugged in, there were no LED's on the logic board.

After replacing the PSU, I was only getting 2 of the 4 Diag LED's on the board. At this point I found a YouTube contributor who had success by replacing the PRAM battery, which I did as well with success. After replacing the PRAM battery, I now get 3 of the 4 Diag LED's to show up.

However, I cannot get the display to work. The screen doesn't flash. It doesn't work intermittently. It's just completely dead.

The Fans in the computer also run really loud. They will start quietly and then gradually ramp up to a high speed. I found a couple posts online about it being a possible HD failure. This morning I removed the drive and connected it to my laptop and am able to read all the data on it without issue.

Other than the fan issue and the display issue, the iMac appears to be powering on fine.

Steps Taken:

• Replaced PSU - Success
• Replaced PRAM battery - Success
• Removed each RAM module one by one - No change
• Validated Hard Drive - Data good

Thank you for any assistance

Also, I inflicted a small crack when removing the screen. There is another crack on the other side that is roughly the same size that has been there for some time without affecting the display.