Using midi keyboard w/ OS2

Sorry if this real basic,

but,

I've got a midi keyboard hooked to the midi in of the mpc.
I've got a multisample instrument program on track 1
I've set track 1 to be a midi type track

It's recieving midi cos when I hit the notes on the keyboard the corresponding pad numbers are flashing up at the bottom of the main screen.
But no sound is comiin out???

It's only one of my progs that's doin this, others work fine.
Any Ideas??