KDE blackouts

[rin fukuda <fukuda med teikyo-u ac jp>]

Hello,

I installed RedHat 6.2J on a laptop (Sharp MN-5600, Trident Cyber 9385 chipset) 
and it works fine with built-in 800x600 LCD in any desktop environments, but KDE
doesn't work when I plug into an external monitor (ADI G700) at 1024x768 (havent
tested for other resolutions).

When I try to login using KDE desktop, the screen blackouts ... Ctl+Alt+Bksp 
didnt help. Other desktops work just fine. Is something differnt in KDE compared 
to others?

The KDE works when I switch back to internal LCD.

Is this compatibility issue or am I missing something in X configuration?

Thanks for your help.

rin
fukuda med teikyo-u ac jp