How come my computers sound does not work for playing music or watching videos?

I recently got my computer back after it being cleared of viruses. But now when i play music or look at a youtube video the sound wont come out of the speakers. However when i turn my computer on it plays that little "windows tune" that plays when it says "welcome". That sound comes out of the speakers so why doesnt anything else?
Check and make sure the little cable that goes from the back of the player is connected to the sound card or motherboard and the player. It's a small cable with 4 pin connectors.
. Check or buy a new cable.
2. Buy new speakers, computer speakers are not the best.
3. Make sure it works.
4. If it doesn't work send it into the company and they will fix the magnetic circuits in your computer.

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