Can't hear MIDI keyboard thru GarageBand (or anywhere else)

I have a year-old MacBook running Leopard, and a Midiman (now mAudio?)49 Keystation USB controller (keyboard). The MIDI setup utility recognizes one MIDI input, but I can't hear the keyboard in Garage Band 3 or any other app I use (Songworks II). I've tried different input settings in Garage Band preferences, System Preferences and in the Audio MIDI setup utility, to no avail. The same keyboard works fine on my iMac G4, running the same software. As I said, the keyboard is USB powered. Is it possible that the MacBook doesn't produce enough power to run it? I have some serious projects to do and would be grateful for help. Maybe I need a newer keyboard? Thanks.