SQL Server Remote Connections

As you've not specifically listed the steps here's some more dumb questions:

1. Have you verified that SQL is listending on port 1433 anyway. Take firewall out the equation initially and run netstat -a -b which should list the service somewhere and tell you which ports the server and browser service are running on.

2. Is the instance name definititely IP\SQLExpress? I've confused myself lots of times when I've installed Express with an instance name of just the hostname/IP of the machine and spent ages wondering why I can't connect when I incorrectly use an IP\SQLExpress host name in the connection.

I previous question similar to this where we finally sorted it is here.

SQL Server Configuration Manager -> SQL Server Network Configuration -> Protocols for {instance_name} -> TCP/IP (should be enabled).

I'm sorry if I appear dumb with my suggestion, it's just not quite clear if it is covered with the list of measures taken by the OP and in the comments.

Also, because this is 2008 R2, the thing has probably been enabled by default, and yet, who knows...