Driver for Sound Device...

Hello,
I've encountered a problem with the sound system of my PC. My Sound device is all right. But no sound is heard when I turn on my PC or when I play any song etc. I've checked my Master volume. All are ok. I think there is problem with the driver software of my Sound Devices. And I've lost my Driver and Application Recovery CDs I was provided with the manufacturers. So my questions are-

1. How to know about the configuration of my PC?
2. How to know which driver software should be installed to recover my sound system?
3. Can I download for the driver software from internet?
4. Which websites are recommended for free driver software?