You'll need to contact GoDaddy and ask them if you're allowed to change the nameservers for the domain, and if so how to do it; we can't help there. The nameservers must be set to ns1.x10hosting.com and ns2.x10hosting.com in order for the domain to work with x10.
Once that's done, you need to login to the account management panel (
http://x10hosting.com/login) with your forum username and password and change your main domain to the domain you bought from GoDaddy.