How do I re-enable my built in speakers on my acer mini laptop?

Yesterday, my speakers were working fine, but today, when I tried to play music from Windows Media Player, no sound came, but this is the message that popped up from Windows Media Player "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 tried to re-enable them using the control panel, but it said there was No audio device. Can someone help me? I think one of my family members disabled it, but I don't know how to re-enable it. Please help me. :(