Can be fairly easy to reinstal the sound driver, the hard part is finding it.
If your pc came with a recovery disc it could be on there which makes it easy but if not and your pc is a common make ie compaq, HP or similar then you can fo to the manufacturers web site and use their 'download and support' link to locate the required driver - more likely than not be something like 'ac97'
Most sites ask for model make and/or serial number of pc so fairly fool proof.
If the pc is home built then you will need to know the make and model plus version number of your motherboard and to do this you'll need to take the side of the case off.
The details you need will be printed on the motherboard (position varies by manufacturere)
Good luck and hope this helps.