The backlight comes on for a few minutes and then turns itself off

I have a Toshiba P25. The backlight comes on for a few minutes and then turns itself off. The display works fine on an external monitor. BUT the strange part is that if you switch the LCD/CRT mode the backlight will come on and then turn itself off. It is as though there is a firmware bug or something. So I reinstalled the display drivers and still have the problem.
I had this problem some time ago and took apart the laptop but found nothing wrong. It then started to work and was fine for several months. Then I was using it and changed the resolution in the control panel on XP SP2 and it immediately sprung up again. Now I cannot get the backlight to stay on for more than a few seconds.
Everything else seems to be working fine.

According to the failure description I would say that you are having a problem with the FL inverter board. It is possible that the screen is bad itself, the video cable is defective, but I would suspect the inverter first. It might be just a loose connection or a bad inverter. To replace the inverter board you have to open the display assembly. If you going to fix it yourself, try to reseat the inverter board connectors first. Just unplug connectors from the inverter and plug them back. Try to turn on the laptop and see if the backlight is working. The next step would be replacing the inverter board. That’s what I would do first. Here you can find more help for troubleshooting laptop video problems.