Can't mute inbuilt speakers

Question

I have reinstalled win xp on my laptop compaq presario C770 TU .I reinstalled all the audio drivers.But now i am facing an issue as inbuilt speakers of the laptop doesnot mute when i connect external speakers and headphone.Previously when i used to connect external speakers or headphone the inbuilt speakers mute automatically.Is there any solution for this ?Your beneficial suggestions will be highly appreciatedThanks