I agree, you need to adjust your DNS. I have an important question for you, though. Do you see your site if you visit the domain without the www subdomain? In other words, do you see the site if you go to "YourDomain.com" and only get the MobileMe login box if you visit "www.YourDomain.com"? If that's the case, you only need to make one change. If it doesn't work either way, you'll need to make two changes.
You said that you host with Go Daddy, but you didn't say whether or not the domain was also registered at Go Daddy. I'm assuming it is and that it's registered in the same Go Daddy account that you used to purchase the hosting account...
Here's a guide that explains how to access the DNS Manager in Go Daddy and make changes: http://x.co/kTW3
That guide can look complicated because there's a lot of stuff that *can* be done in the DNS Manager. In your case, you probably just need to access it and choose the "Restore Detaults" option for your CNAMEs. To be sure, though, it's always best to contact Go Daddy Support so they can go over the exact details of your account with you and make sure you're not making any unwanted changes. They're available 24/7, so you can call whenever it's convenient.
If the site's not coming up without the "www" subdomain, you should also change the nameserver setting. To do that, read this guide: http://x.co/kTXR
You'll want to follow the steps for "Setting Nameservers for a Domain Name Registered with Us" and choose the "I have a hosting account with these domains". It'll take a little time after you make this change, but our system should automatically set the domain to point to the hosting account properly.
I hope this helps. As I mentioned before, don't hesitate to contact Go Daddy Support for assistance. They're better equipped to instruct you since they can look at your account settings and walk you through making changes. Phone and email contact info is here: http://x.co/kTYi
Good luck to you!