Dell latitude c640 audio problem

what u should do is
turn off your system
press and hold Fn key,power on the system, leave Fn key
computer will perform a diag
after those diags you will get 4 options you have to choose symptom TREE
you will get options look for any option which says sound or audio
if you hear sounds at that time you need to reinstall the drivers as it states that sound card is working fine
or else
provide me your system's service tag located at the bottom pannel of your system, turn it upside down you will find a bar coded sticker which has a 7 digit alphanumeric number
it will be much more easier for me to provide u a resolution