Airport card in powerbook G4 Titanium 550

Hi, Malko. Open Apple System Profiler and look in the "Airport card" section. You should see the card listed there. If you don't, remove the bottom cover from the Tibook and follow the removal instructions here. After removing the card, reinsert it in its slot and make sure it's firmly seated. Then (this is the important part) press down hard on the rectangular plastic tab at the end of the tapered ribbon cable that's connected to the Airport card slot. That's the card slot's connector to the logic board, and it's possible that you loosened that connection in the process of installing your card.

If Apple System Profiler still doesn't show the card after you've reseated it solidly in its slot and made sure the slot is well connected to the logic board, you may have to conclude that the card is dead.