Try using a new VGA cable (connects computer to CPU)
Also, for no sound coming from the speaker, this could be due to something in power supply or in the ports. Open up your computer. Go to the power supply (the big box with colored wires popping out of it); make sure it is connected to the harddrive and motherboard.
Next, look for the gray sets of wires (looks like a flat, plastic gray thing; one wire should be colored); make sure they connect to the motherboard (on the ISA slots), and make sure they connect to the harddrive. When connecting them, they can only go in one way: if you look at the pins on the ISA slots, there is a space with none; make sure the space with no hole on the connector lines up with that.
If none of this works, make sure your slots are firmly connected in some way to your motherboard (even through another board); if none of this works, I recommend bringing it to a shop to get it fixed.
Taking a class for A+ certification (in layman terms: I will be able to fix computers)