Problem with media control button (XPS M1530)

Hello!!!

I have a laptop XPS M1530 with Windows Vista.

My problem is that the media control buttons are not working.

I can't change the volume, or make a play/stop...

I have put the new drivers (Dell Quickset), but the buttons still not working.

But, if i use the MediaDirect Button when the laptop is shutdown, the buttons work well

And when I close the lid of the laptop (mode suspended??) and then the open sometimes the buttons work well.

what can happen????

Thank you and sorry for my English...