Need help in fixing sound please!

Hi. Ive really tried reading in every forum online Ive found how to fix my problem, but none of them applied to my case so Im sorry to finally be bothering people about it.

The thing is that I bought this used Fujitsu Siemens desktop some weeks ago with Windows 2000 in it, however when I upgraded it to Windows XP Home, sound stopped working at all. I know my speakers work, however no sound comes out from them when I plugged them to my computer. I dont really know much about drivers or codecs, so I wouldnt know what else to specificate, but I would really appreciate someone could help me on this one, since Im here in a new country and with no music. tragedy tragedy hehe.
Thanks!