Cinema Display 20" stays dark after computer start

Hi

I have a *PowerMac 400 MHZ (AGP Graphics)* (OS 10.4.10 with 1.25 GB RAM)

+ http://support.apple.com/specs/powermac/PowerMac_G4AGP.html+

And one new *Cinema Display 20"* (DVI conector)

+ http://www.apple.com/displays/specs.html+

The graphics info on my System Profiler say

ATI Rage 128 AGP Pro (VRAM 16 MB, VGA + DVI connector)

But when i turn on the Mac, i see the Apple logo loading and then, when i must see the OS blue bar loading. The screen stays dark.

I can hear ths sound feedback when i press my keyboard. But no image.

Any suggestion?