You reinstalled what? Windows I presume, if so so you have your motherboard disk and have you installed that yet? If you have onboard sound the drivers for that will also be on the motherboard disk. If you have a seperate sound card you should have a disk for that.
If you don't have the drivers then if you give some more info someone will be able to tell you where you can get them, we will need to know the following. What Operating System - windows XP, windows 98 etc. What make and model your motherboard is and if you have a seperate sound card what make that is.