no audio output device found message

My computer was working with sound so I don't know what changed.I have an insperion one 2305 and now I have no sound.  The notification says no  audio output device installed.  I don't know if it is the same problem, but I cannot view videos on utube either.  I get a black screen that says an error occurred.  I have tried to install drivers and that didn't help either.  I'm kind of a rookie so in plain English would be helpful.