There is _no_ question that you damaged the card initially, reverse protection diodes
dont just fail (along with both driver chips on the same power rail)
The driver chips passed a digital loopback at 24V but on further examination did not swing fully to 24V
so this was missed on the first return.
If 5V and ground are truly shorted its likely you damaged the 5V side of the card also
I was kind enough to repair a card that had been abused as a warranty repair, I will not do it again