Problem with sound card recognition

I am using an AMD Athlon 3200, 1GB Ram, Realtek, Firefox 8.0 with a High Definition Audio Card. Sad to note, however, that the said computer does not recognize the sound card. It seems that the sound card doesn’t exist at all in the said unit. Whenever I search the web, play some audio or video files, there is no audio output. I can’t hear anything even though my speakers are working well. I’ve already tried searching the solution in Google but I cannot find anything that works for me. It’s really very disappointing. I feel crazy about it. Please help me to solve this problem. Thank you.
