I'm helping a friend set up a new IMac computer running Lion. Everything was going OK except for the password. For some reason the password box appeared and we put in the password, but it kept saying it is not correct. With the help of another friend we changed the Apple ID and password. But now whenever I try to install software (printer), etc. a box comes up asking for the password. The ID isn't the one we chose and the password doesn't work. We cannot install anything. How can we correct this? And why is this appearing when I try installing apps?