Likely just a driver problem. You don't give any details so I'll have to ask you a few questions.
Does it happen with both speakers or just one and what is actually happening?
Does the sound problem also happen with a headset?
If yes have you tried uninstalling the drivers for your sound card in the Device Manger?
Don't click the "Delete the driver software for this device."
Then click "Action" drop down menu and select "Scan for hardware changes".
Windows should then reinstall the drivers.