One possibility is that the audio cable coming from the speakers isn't correctly plugged into the audio-out jack of your computer. The volume may be set too high, or the audio file you're playing back is corrupt. The sound card may be broken, or the driver software is corrupt. The worst-case scenario is that the motherboard has an electrical fault. Use a process of elimination to pinpoint the source of the problem; it will help you decide what needs to be done. The simplest test you can try is to turn down the volume. Try playing a different audio file. Next, try unplugging and then plugging in the audio cable coming from your speakers. Use a different pair of speakers. If they work properly, your sound card is probably not the cause. Replace the speakers.
They're probably blown or damaged. You must've turned it on too loud for too long. Try keeping the decibel lower (when you get new ones). (I understand that some people like to "blast their speakers up" to escape from everyday stress, but running away from your problems won't solve them. Just saying.) I hope I helped you.