Before you reformat try this. Your motherboard probably has a built in sound card. Download the drivers for your motherboard and reinstall the sound driver. If this does not work, get professional help.
Try going to device manager and roling back the driver for your sound... also just to be safe check your volume levels and make sure everything is turned up and nothing is muted search for hardware also make sure your mobo is picking up the speakers try puting in your backup disk for your audio ( the mobo disk, audio card disk, or the disk that came with your pc) going to add hardware in control panel it will ask you a question pick yes, it will search for hardware make sure everything audio has no errors if it does select it and use the disk to install/ repair it.
. I've had this problem a few times and theres a thread with all the things i've done to fix it check out this thread:http://www.techspot.com/vb/showthrea...t=34244&page=2 maybe it will help.
sorry for grammer or spelling its been a long day and i've had no sleep