A common issue I’ve seen is when the systems power is fully removed, so the NVRAM battery runs down as the system is designed to leverage vampire power from the AC connection. Make sure you don’t have a switched power strip which you turn off most of the time. That might have been your original issue.
The other issue I’ve seen is the Fusion Drive breakdown. Which requires both drive elements be removed.
It does sound like your heading that way, I’m not clear if you’ve pulled both the HDD and the blade SSD which is the cache drive within the fusion drive set.
While you could indeed have damaged something in the process I don’t have enough here to isolate it down.