If you just signed up and your email stopped working it is likely that you have a domain name with another company and you updated your name servers with them. Once you update your name servers your domain name and email start going through our servers. That means anything you have set up with your current domain resgistrar will stop working.
You will need to set up your email accounts within your client area. To do this, follow these steps;
1. Login to your client area here
2. Go to Services->My Services in the navigation bar and select 'View Details' next to your domain name
3. On the next page press the button labelled 'Email Accounts'
4. From this new page you can create your new email addresses
This is also illustrated in this video tutorial:
If you are using Apple Mail, or any third party email clients, you need to update your settings for your email accounts as described here.