Tascam US-122 problem

I am trying to use my Tascam US-122 as an input for Garageband '08. I downloaded the driver from the Tascam site and GB recognizes it as an input device. I set the preferences for a live instrument, the input as the 122 but when I start to record, I get no signal in GB. The 122 shows a USB and a signal when I play an instrument or speak into the mic. I have tried using a microphone and a guitar in either side of the 122(not together). Nothing seems to work. Can anyone offer some guidance? I am using a new MacBook.