Mike,You might try one of the following when entering the server name. Unless you manually changed the default settings you will have an instance name and TCP/IP will be turned off. So you will want to enter a server name like this:
MyComputerName\SQLEXPRESS
You can also try this in the case the TCP/IP is turned on:
localhost\SQLEXPRESS
Finally, if you installed SQL Server as the default instance, then you can omit the SQLEXPRESS instance name (this is not as likely if you did not do this intentionally):
MyComputerName
or (if TCP/IP is enabled)
localhost
One of these should more than likely work.