Help anyone: Connected my MacBook using DVI adaptor with Dell 2408WFP monitor but can only see screen saver - nothing else?

Hi 

I have just received my new Dell 2498WFP monitor that i have connected with my MacBook using DVI adaptop but i cannot see anything on the screen except the screensaver - i have also connected the USBs but its not working!

Please can someone help resolve this?

Thanks

Zaheer