Toshiba Satellite A100 PSAA2C video boot

I have a Toshiba Satellite A100 PSAA2C. The laptop displays boot up only on external monitor. When re-installing loads of drivers (all type of display drivers), I can finaly get the laptop screen to display. Next reboot or start up, same as before, like it erases the drivers and settings. The laptop doesn't even show it has a screen and only displays on monitor.

I have re-intalled the OS from the cd that came with the laptop... Oh and yes, I have changed the fl inverter, I did the think about removing all power source and rebooting. I also updated the BIOS to the latest version. As I mentionned before, it's like the set up is being modified even after I re-installed WinXP on it. In the process of installation, the display comes back on the laptop screen and then goes out, only to display on external monitor and back again. That what makes me believe it's software related.

. 1 out of 3 times I have the right display. How to get it every time?

The screen is working fine (when it displays), everything else is okay with the laptop.

I hope you can help me with this. Thank you