Sound comes from a pinout on the motherboard. Maybe you bumped the connector and now it's loose or dislodged. Consult the manual for your PC or motherboard and see if you can find it. Alternately, open the PC back up and look carefully inside arount the lower edge of the motherboard for a loose connector - that's usually where the connector is located - to the left and bottom of the motherboard when it' in it's usual mounted position. It may, of course be in another location as well.