constant audio activity

hi, I have a Lexicon Omega interface and i’m using it with cubase LE5.
When i connect the interface, and select the device in cubase, the audio activity indicator lights up in red.
and when i import a song and listen to it via my headphones, there is more noise than sound.

who can give me the solution to my problem? i’m using a macbook pro for cubase.

thx !

What operating system for Mac are you on (10.6, 10.7, etc)?