Latitude XT backlight issue

Hello all,

I have a Latitude XT running Vista which has a strange issue I'm hoping someone can help with.

When the machine first boots up, the backlight is not turning on.  Nothing turns it on until the laptop is signed into.

I've looked at power save profiles and the auto brightening options but had no luck.

Has anyone else seen this or could anyone suggest any other ideas?

Many thanks,

M