Changed main domain with host and lost my site

Hello all. I am needing some help to get my site back on track.

I have a WPMU install with buddypress which is integrated with BBpress.

Due to some business changes I had the host (PSek) change the main domain of my account and now I can not access my site at either domains.

When I go to the new domain that is being used for my account I get the following error-
Access is forbidden to the requested page:
crosseyedgamer.com/wp-signup.php?new=crosseyedgaming.com

Note, I went from crosseyedgamer.com to crosseyedgaming.com.

If you pull up crosseyedgamer.com now you will be going to my current live site on a totally different server so do not even pay attention to that. I was using the install on the PSek server as the new site and thought we were going to use the same domain. That changed and I thought if they changed my account info I would be able to then change things in WP and database myself.

I can access the database and I saw a tutorial online about changing the site urls in the tables which I am ready to try but before that I wanted to see if anyone else had some tips for me.

I don't want to go messing with the database and other settings and end up with a totally wrecked site.

So to sum things up, Same host, Same IP, different domain name. What is needed to get it working again?

I appreciate your help.
Thanks.

UPDATED INFO -- I went into the wp-config.php file and change the site domain to the correct one and when I go to the site now I get the following
Firefox has detected that the server is redirecting the request for this address in a way that will never complete.

I cleared all cookies and everything and tried again but got the same thing.

Wasn't sure if this would help with trying to get things worked out or not. Thanks again.