My wife's computer lost sound about 2 years ago. I worked with a Windows XP Escalation Engineer who took me under his wing so to speak. Her system is a Systemax with licensed software for their proprietary systems: no windows disc came with the system. If you go to controll panel > sounds > and it is grayed out and defaults to a modem that you may not have installed, the issue is a dropped Windows driver. To fix the problem get a "clean" windows disc. If you don't have one Microsoft will send you a replacement. The Utilities disc manufacuters send with their systems ~ will not work! In save mode insert the disc and check "Repair"; be sure and check your BIOS to see if it is set to auto start [yes]. The disc will reload all the drivers necessary. Be sure to down load new audio drivers [Audio 97 or disc prompt] to a folder on your desktop - it's easy to find there. While the repair is patching files, for each file that it requests a disc to be inserted to load a specific dynamic link library .dll file, make note and download those as well. After you are prompted - reboot, and download those files that the Windows disc asked for during repair. Once you have downloaded and installed the requested file updates, reboot and your problem will be solved. Just a note: systems with factory installed Windows are problematic and without a legit version of Windows XP, your problem is there to stay. My only problem now is keeping my wife's volume turned down....If I can be of further assistance let me know. That problem was persitant.