Hi Bob, emachines are simple (reliable) systems so when you can see the system playing music but aren’t getting sound from the speakers it will be one of these:
• Make sure that the speakers are turned on.
• Make sure that the volume controls are turned up.
• Make sure that mute controls are turned off.
• If you are using external speakers, check your speaker connections (the green plug) and power... try putting the power plug in a different slot.
• Make sure that the universal jacks are configured correctly. i.e. if you (someone) opened the box, then perhaps the lead connecting the jack plug to the motherboard hasn’t become unattached… I normally consider this least likely but you have stated that you have...