The display on my Inspiron 8100 is up to no good. At certain times, the backlight does not function. This is reproducible. Here's the situation:

Running on battery power: Starting from a cold boot, the backlight functions normally. Rebooting, the backlight still functions normally.

Running on AC power: Starting from a cold boot, the backlight functions normally. HOWEVER, on a reboot, the backlight turns on at post, flashes once, and shuts off. It does not come back on. The display is on, just no backlight. If I close the lid (machine goes to sleep) and open it again, the backlight comes on.

I have so far:
Flashed the BIOS to level A15
Updated nVidia Geforce drivers
reformatted and clean install of XP Home, applied service pack1 and all patches.
Disconnected the reserve battery to reset BIOS.

Still no joy. Dell's tech support has not been able to resolve the problem, although they have tried hard to understand the problem. I have not yet been able to convice them that this is not a software issue.

Any suggestions?

Thanks