As Huracan stated, it would help to know Which Operating system you are using, like windows vista, windows 7 ect...
You can depending on system, click the start/search button and type "Device Manager" into it, once you pull up the device manager, look for "sound,Video and Game Controllers", click the "Plus Sign" next to it, and it will drop down a list of drivers, your sound driver will be in this list, it will be something like "realtech high definition audio" ect.. Is there an exclamation mark next to the driver?If not you can left click the driver once, then right click it and chose "properties" inside properties, it will tell you if the "device is functioning properly"
This would be the first place to check for an issue with your sound.
Once you know your system is clean and free from malware and have the issues settled, we can show you how to stream line the restore points and defrag for optimal speed.