Dell 640m got a distorted display in external monitor after upgrading to 10.6.2

[frankmail007]

I managed to install 10.6.0 retail version in my Dell 640m laptop without many problem except the resolution is only 1024x768 ( mine can support 1440x900). So I decided to upgrade to 10.6.2 because somebody told me it could solve the problem. But I got a black screen after I upgraded to 10.6.2. So I tried to connect my laptop to external monitor. This time, I got some display in the external monitor. But the display is totally distorted so that I can't do anything because the mouse cursor always point to the wrong place and only a small part of screen is shown ( the screen shrinked horizontally and strectched vertically).

 

I think it could be the problem of the display driver so I boot in Single User mode and delete all AppleIntelGMA* in /System/Library/Extensions. But the problem still exists. Then I tried to boot with "Graphics Mode"="1024x768x32". Also doesn't work. At last I tried ?video. To my surprise, everything in every mode are 0. That means all the resolution supported are 0x0x0.

 

I got totally lost. Does anybody have any suggestions on this? Thank you so much.