21.5" iMac screen displays a very faint Apple Logo after hd swap

I replaced the hard drive in my late 2015 iMac 21.5” Per the iFixit instructions, I tested the unit before permanently sealing the screen to its back.

The screen does not display anything EXCEPT for a very faint pulsating Apple logo. My local uBreakiFix store got the same pulsating logo using a different monitor but could go no further. Reinstalling the old hard drive resulted in the same results.

Any ideas?

Thanks in advance.

Some system specifics:

Apple iMac 21.5”

Late 2015

EMC 2889

OS 16.1 Monterey

V12.7.3 (upgraded 2/20/2024)

Processor: 1.6 GHX Dual core i5

I5.5250u

Ram: 8GV 1867 MHz DDR3

USB 3.0 (four ports) 5gb throughput

Thunderbolt (two  ports) 20GB throughput

Storage 1TB SATA Drive  910GPAV