After repair iMac fans spin but no display and no chime.
I replaced the HDD with an SSD (formatted) reassembled everything in its bare state, it turned on and chimed. I fully reassembled it, fans ramped up but nothing on the screen. Checked all connections. Reseated GPU and CPU. Reset SMC. No beeps. Nothing. If you’re curious, there were 2 lights on, one indicating that power was connecting, the other indicating it was powered on.