I've just formatted my acer aspire 4520 and

Assuming you were not experiencing issues with the sound before here is a good start for troubleshoot:

1. Go to the device manager and confirm the sound card device is list there as working correctly. Also, go into the properties of the device and compare the driver version installed to the version you downloaded. Be sure they are the same and that an older driver was not picked up and installed instead.

2. If your driver appears to be installed correctly with the right version number then you should double check to be sure you have downloaded the correct driver. After you are sure your driver is correct you should delete the device from the device manager and reboot. This will cause the OS to reinstall the driver and is sometimes all you need.

If after these steps your sound still does not work then please post the driver you have downloaded and the filename along with the operating system you are running for further troubleshooting. Assuming you are running windows XP this should be a working driver that you can download at this link http://www.mediafire.com/?tylmvdn5gzj .