do you mean other computers in your house, or other computers elsewhere with different internet service providers?
If not, it's probably a DNS propagation issue. When you type a name of a website into the browser, it the machine asks it's DNS server "what's the IP address of <web address>". Each ISP has it's own DNS server so when your friends access the website, they are asking a different machine what the address is. As mike says, give it 48 hours from you changing the address for it to propagate and then contact your ISP if you are still having problems.