For Video cards - Most PC video cards these days are AGP. But you COULD be working with PCI, or PCI express. If you're not sure which you have (more then 75% of the time it will be AGP) consult your motherboard manual. If your video card is AGP, you should see a slot smaller then the other slots on your board, and it will be a different color. You can likely also tell your video card if it has a GPU (a processor with a fan on top of it) or a video card company printed on it like Nvidia or Geforce.

To take out your video card in order to switch it for a newer one, or if it simply is not working, remove the screw first that holds it to the case. DO NOT ATTEMPT TO REMOVE THE CARD UNTIL YOU HAVE UNSCREWED IT. You will damage, maybe even destroy your card, and you may damage your AGP, PCI or PCI express slot as well. Your board may then have a simple switch that holds the socket down. Flick this switch up. After the scrue is removed, and the switch is flicked up, pull the card away from the board. Pull it on one side first so when it comes out it comes out on a slant, kind of like a car reversing. It should come out quite easily. To put in a new card, make sure the card you're putting in is properly lined up in the slot, then press the card into the slot. If it dosen't seem to be going in, you may be putting it in the wrong way. The pathways on the one side of the card should be the side that goes into the motherboard slot (these pathways looking like small lines going up one side of the card). Once the card sinks in with almost a click (like RAM), flick the switch down and scrue the card into the place you unscrued it. Start up your PC, make sure the card is working, then put your case back on.

Sound card - Sound cards are pretty easy, and the method for these can be used for any other card, such as network cards and the like (assuming they are all PCI. PCI are the black slots on your board). For installing/removing a PCI card, just unscrue it from the board, pull it out, then put the new one in, and scrue it in. Pretty easy. If you are having troubles, make sure the lines running up one side of the card is the side going into the slot. If you still have troubles, try turning the card around (but still make sure the pathways are facing the slot).