LCD backlight lamp problem?

Hi all,
I've a TOSHIBA M65 Satellite laptop.
When I turn on the PC the LCD backlight lamps work only for few seconds.
Straight after the screen gets dark. The LCD is working because I can see Win XP running, but the backlights are turned off.

I changed the inverter but I still have the same problem.

Could backlight lamp works only for few seconds when broken?
Could be a driver or motherboard problem?

Thank you very much for your help!!!!