Apple Logic Pro /LogicExpress Discussion

I'm only a beginner to all of this having been happy with sonar and reason before i've had 
to move up (as it were) as my pc can't handle the load anymore. 
So, my problem is probably straight forward but i can't figure it out. I've got an M-audio 
keystation 49e keyboard connected to a 17" G4 powerbook via USB. When i open logic on 
its own it picks up i'm playing something and will record the notes in the midi tracks but 
won't play anything back. It's almost the same with reason but i understand that i'd have 
to sort it out in the environment *cringe*. 
That's probably where the problem is.
Tried looking at the environment, had a go. still nothing.
Any advice would be much appreciated!
Thanks