Also, do you know what brand/make of motherboard you have? If its a chain bought system (Dell, HP, etc...), what make and model is it?
One think you can check is to make sure you have one of your drives jumpered as a master and the other as a slave. You can check this by looking at the back of the drive (where the IDE cable plugs into the drive) and there is usually a little diagram listing what jumper should be set for each setting.