Sound Problems

Hello,

On my Comapq Presario Laptop[with Vista],I cannot hear any sound from my laptop speakers.But when i use headphones[with the right jack plugged in] I am able to hear the sound without any problem.I even uninstalled and reinstalled my sound driver also.But the problem still persists.This problem occurs very frequently on my laptop.Sometimes after few days donno how i will be able to hear sound directly without headphones properly without any problem.

Will be very helpful if anyone suggests a solution.

Thanks
Uday