VAIO PCG-K33 display goes blank during windows boot

Hi All,



My Sony has a problem that I can't seem to fix so I'm looking for

help.



When I power on my laptop I can see the Sony logo, I can get into BIOS

and I can load MS Memory Checker and still see everything on the LCD

screen. I will call this text mode.



Once the HD begins to boot, before I get the 1st loading Windows XP

screen (the color screen with the little bar graph) the LCD goes blank

(the backlight goes off, I see this because I have taken off the

bezel) but the external monitor still shows the progress. I will call

this graphics mode.



I have swapped the LCD screen (with LCD cable attached) and I swapped

the inverter board, both came from a working laptop of the same

model. I see the same result, once graphics mode starts the screen

goes blank and the backlight turns off.



I then installed the LCD screen (with LCD cable attached) and inverter

board that I just removed into the known good laptop. This time the

LCD screen works fine. Both text and graphics mode work as it should

and Windows XP boots fine and I can see everything on the LCD screen.



I have the laptop set to display on both the LCD screen and external

VGA monitor, both laptops were checked and the setting on both is

correct.



It is not a driver problem because I also swapped hard disks and I get

the same results.



Can anyone suggest anything else I might check?





Thanks for any help,



Charles