Error - No screens found

Hi,

Recently I have installed Redhat 9 and mandrake 9 on my system. But after 
completing the installation part, I am not able to get into GUI mode as 
the error message says that "No Screen Found".

My system configuration is 

Asus P4V533 motherboard
P4 - 1.7 processor
ATI Radeon 7000 64MB DDR Video card
Samsung Syncmaster 753S 17" monitor

I feel that the problem is with video card drivers. I am getting same 
error message in both distributions.

I am really looking forward for your help. Plz send me the detailed 
information to get rid of this problem.

Thanks alot

Regards
Prem Kumar Madala