Anything is possible at this stage.
The diagrams I've seen so far have the jumper/bridge wire either + + + or - - -.
It theoretically suggests there that you were more or less bridged - - +. There is a chance it could've had some kind of conflict on the drivers.
BrianPM is talking about this wiring:
Then label Enable disable rather than confuse it with a +5v connection that you did. Sounds about right.
https://www.cnczone.com/forums/attac...d=424664&stc=1
I don't know about a way of stand alone checking of everything tbh.
I think you're best bet is to just hook up the DB25 board to the Dell PC and a power source. Then run some cabling to one of the drivers and see if you can spin it.
You could throw this together fairly quickly outside the box for testing and leave the driver where it is.
If neither one of these 3 wiring setups work then chances are your drivers have pooped imo.