Did you say you upgraded from vista to win7 and lost sound?
If so did you try checking the ACER support website for win7 drivers for your MB/Chipset? That would include audio drivers.
If Acer does not provide win7 drivers then run Windows Update. Win7 will try to find the drivers you need. It might guess wrong, but that will give us a starting point.
Win7 32 or 64 bit ?