Very Confused W/ Virtual Instruments Options

[JOLTINJAKE]

hi, i have an edirol midi keyboard hooked up to an imac, and the imac has cubase on it. i also have an MAudio Duo hooked to the computer, which i can use for recording live instruments. now heres where the trouble starts.. when i try to record midi music onto cubase with the edirol keyboard, i see the little red and green bars showing the incoming signal, but no sound comes out.

someone recommended that i check my virtual instruments, but after reading the manual, i still have no clue what to do. i think cubase has some built in bass and percussion virtual instruments, and i thought i had those set up right, but there was still no sound coming out. ive tried selecting all the different output options it gives me, but still no sound comes out.

if anyone knows anything about this stuff, please help me!!

do i need to download/purchase virtual instruments from somewhere? am i missing a piece of equipment that allows me to hear the music?

thank you very much for any assistance you can give!