The problem solved...

Thanks to this thread, I realized that the problem was my graphics card temperature. And I should've guess coz my fingers burned when I played WoW. The card was hitting 100-105C !!

For now I play in 1280x800 windowed mode with a game CD box to elevate the screen end of the laptop. I take the CD ROM out for more airflow. Thanks Dell for this facility.

So I got to get the card cooled properly and I am done.