Onboard sound doesn't work

Question

I've a emachine 770 pc.the motherboard went dead and i replaced it with a ASrock P4VM890 motherboard.I changed the agp graphics card for a pci radeon and the psu went after i installed the motherboard.however, the internal wire from the internal speaker doesn't connect properly to the sound connector on the motherboard.this doesn't bother me.the problem is the onboard sound where you connect the speakers seems to play but no sound is coming from the speakers.it has the latest driver as well.using windows vista standard.any ideas?