As a disclaimer, I'm new to digital electronics and somewhat new to soldering.
I recently bought a standard GPIO header for my raspberry pi zero, but in order to use both the camera part of my case and the pins, I soldered the pins up from underneath, rather than from above down. So the short pins are soldered on the top of the board instead of underneath like usual. However, I tried using a screen module on this, which only showed up black but shows up in full display on the other pi zero I soldered in the traditional way. My T cobbler also works on the normal one, but not on the one soldered upside down.
What could be the possible cause for this? I tried reversing the orientation of the ribbon cable from the Pi to the T Cobbler and that showed power for a brief second before dying off.
Again, I'm extremely new to this sort of thing since my specialty is programming, so I'm not sure how to diagnose these sorts of issues -- I do have a multimeter, as well if need be.