Before you can remove an expansion card from your computer, you have to make sure that everything connected to the card from the outside of the computer is removed. This is usually a good step to complete when opening the case but if you haven't done so yet, now is the time.
For example, if you're reseating a network interface card, make sure that the network cable is removed from the card before proceeding. If you're reseating a sound card, make sure the speaker connection is unplugged.
If you try to remove an expansion card without disconnecting everything attached to it, you'll quickly realize that you forgot this step!
