Sound doesnt play on Windows 8 laptop

[htr63]

Recently my laptop starting having issues playing sound. I've had it for over 18 months now with no problems whatsoever. However my sister used it for a project a couple of weeks back and ever since then the sound will just randomly stop playing with no apparent cause. She insists she never did anything to it besides searching a few things up on the internet. Also, if I click on a file in Windows Media Player after the sound has gone, then a red X mark appears on the next 8 songs, and a message pops up saying 'Windows Media Player encountered a problem while playing the file.' The problem is solved for a short while by closing and reopening the lid. Also this problem doesn't seem to occur when I plug it into an external monitor using an HDMI cable. Because of this, I wouldn't really have an issue, but because use the laptop at school a lot, working speakers are kind of a necessity. Headphones and external speakers don't work either while the sound is off. The laptop is an HP Envy DV6 running Windows 8.
Anyone has problems similar to this?

 

[masmotors]

maybe a downloaded file or uninstalled driver maybe you got a buggy bug

 

[i7Baby]

She probably changed settings.

Check your sound controllers and working OK in Control Panle, Device Manager.

Check your speakers are enabled in Control Panel, Audio Manager, Playback.

Check your audio vols are up by clicking at the top of the volume slider from the bottom RH side of desktop speaker icon.