low battery warning does not appear

Hello,

I am running Vista on a laptop computer. Although I set it up in the power
settings that I should get a notification when the power level drops to 10%,
this notification does not appear (anymore). This happens with every power
mode I select.
It does not help to turn the option off and on again.

Does anyone know what I can do to make the notification appear again? It is
annoying if the laptop goes to sleep mode only because you have not pluged
in the AC adapter in time due to the missing notification...

SAP