Where do i get a sound card from?

Hii

well....

I Formated my computer because of an awwwful virus. and i reinstaled windows XP.
the thing is...that i can't hear anything from my speakers.

Everytime i try to play a song on Windows Media Player a message comes on screen saying:
"Windows Media Player cannot play the file because there is a problem with your sound device. There might not be a sound device installed on your computer, it might be in use by another program, or it might not be functioning properly."

I went to Sound and Audio Devices Properties and it says:
"No Sound Device".

So i went to the Diagnostic Tool
and it says that:

"No sound card was found. If one is expected, you should install a sound driver provided by the hardware manufacturer."

Well....this is actually wrecking my head...because i don't know the right sound card to instal + i don't know where to get it from. I'm not blonde but i am kinda dumb at this "computer" stuff. xD

hope someone can actually help me out with this thing.

Cheers

Peacey