New AD524R is not working

I recently bought and tried using the AD5624R with an Arduino Duemilanove board.

I make sure I supply Vdd and Vref with 3.3V DC and I supply my circuit with 12V DC.

For ground I use the ground of my DC Transformer.

For the SPI I connected Pin6 of the DAC with the SS, Pin7 with SCLK and Pin8 with MOSI.

I uploaded the four sine wave example code and I got no results on the outputs. I measured directly on the output and ground.

Am I doing something wrong? Is an opamp necessary for the measurements?

Is my DAC broken?

Can you please give me any suggestion?

Thank you in advance!