Sounds like a hardware issue to me, because if it were a software one, the new OS (Ubuntu) would load the driver & sound would be up & running. Ubuntu or any other Linux based OS is totally independent of Windows, those OS's finds & installs the needed drivers for your system to run.
If you feel comfortable in doing so, you could open the computer & make sure that wires/plugs are intact.
Here is the page where your drivers are (you may need to select your model again). Audio is the 1st driver listed & for XP, should have everything you need, for that OS.
I second hamluis, it's bad practice to download files from the Internet, as who knows what's bundled in them? As in malware/other infectious code that can damage not only your computer's OS, but also monitor your activities & potentially steal your identity. Most OEM's carry at least the original drivers on their home site for years after the computer is shipped.