dell-dh

I got an old computer from a small business that had a network, but now I don,t. I want to add a user name and it said that it could not find the network. I am using a old user name that has admim permisions, (I am not logged in as administrator, I don't know that password) but it will not let me add a new user. Can I just remove the old network and it will let me add a user.
dh