Locate the audio/video connections at the rear right area of the motherboard. There should be six bent strips of gold metal connecting to the motherboard. For unrestricted access to the A/V area, remove the plastic plate above it by unscrewing the left and right screws. After unscrewing, lift the motherboard a bit in order to pull the plate off.
Heat up the small contact (between each strip and the motherboard) with a soldering iron. For best results, heat all 6 contact points so that they become soft and moldable, and then allow them to dry and reform a solid connection.
Heating it and letting it reform will potentially fix any oxidation which could prevent the flow of electricity, so let the contact reform and dry, and then reattach the plate onto the 6-prong area. Test the output for correct video signal and/or audio signal (depending on which problem was occurring).