Hi all. i just recently acquired a Dimension 4500.  it's a little old and when i received it, it had no operating system at all on it. i installed a 2002 version of XP professional on it.  everything seemed to be working fine, until i tried to turn the volume up.  There is no volume.  i have no sound.  i have tried two different sets of speakers and neither is making a difference.  what do i do?