ADC Cinema Display goes black with dual 500MHz G4

Help needed: I am trying to replace an ADC Studio display with an ADC 20-inch Cinema Display on a 500MHz G4 tower but after a brief startup it goes totally black. I tried starting up from OS 10.1.5 or 10.2.1 without success.
Otherwise, the Cinema Display works perfectly with a dual 1GHz mirrored-door G4 that is running 10.2.6.
Please help...
Thanks,
glegr

System Profiler says ATI Rage128Pro. Card ROM# 113-7201-136.
Thanks,
glegr