I am using a Dell Dimension E521 on Windows Vista Home Premium with Internet Explorer 9. The sound used to work, now it does not; I don't know  why. I have checked both ends of the connections and they are snug. I made sure there was a green light showing on my speaker and that the volume is turned up. From the Device Manager everything appears to be on and working, however I have no sound. From fireberd's answer on Jan. 25, 2010, I was looking for something  else I could check. Even though the sound is being detected in Device Manager, I thought that perhaps resetting the BIOS would be a good start but I don't know how to do that. I did recently upgrade to Internet Explorer 9, at least theoretically. That is to say that a computer tech said she installed IE9 when she did some work on my computer but from time to time, an IE9 dialog box would come up suggesting I upgrade, so I "upgraded". Could this have anything to do with why the sound quit? I'm totally lost; can someone please help?