I'm confident that you've simply failed to reinstall the sound driver. If you can tell us the exact make and model of your PC we can direct you to the download you need. (Once you've downloaded the file you simply need to double-click on it to install the driver, then restart your computer and enjoy sound once again).
If you can't specify an exact make and model, download, install and run Belarc Advisor. That will tell you the make and model of your sound card (if your PC's got one) or of your motherboard (with on-board sound). Then tell us what you've found out.
http://www.belarc.com/free_download.html