Nuendo set up problems!

Hello Everyone! i have Nuendo 5 and i am having the issue that when i create a new track, and for example i want to record a bass directly with the laptop sound card, i plug it and the laptop recognize it but there is not sounds comning out of it. And the strange thing is that the internal mic of the laptop picks up the sound instead of the bass!
Can anyone tell me what am I doing wrong? obviously i am no expert on this…
Thanks people!!