Are you sure there was not a white and black wire hooked up to the card when it was in the original case?? Those wires are the antenna leads, sometimes the antennas are embeded into the case (just like how they are hidden behind your laptop screen) so you wont actually see a dipole antenna in your case.
The 95% likely chance is that the old case had those antenna wires and the new one does not. I have diagnosed a few laptops where those cables come unpluged; when they do the laptop has to be in arms reach of the router to get a 2-3 bars of signal, move 5 ft away in the same room and you are lucky to get a signal at all, add a wall or a floor to that and you get nothing.
If you have a drill then just take off a PCI slot cover in the...