Building up on Steve's suggestion I would like to suggest that you can try using the following to forcefully use TCP/ IP as a protocol:
1) For Default instance, you can use TCP:Hostname to connect to SQL Server.
2) For Named Instance you can use TCP:Hostname\Named instance to connect to SQL Server.
If SQL server is not listening on default port = 1433, you can also add the port no as a suffix if you have not created a alias
1) For Default instance you can use TCP:Hostname,portno to connect to SQL Server.
2) For Named Instance you can use TCP:Hostname\Namedinstance,portno to connect to SQL Server.
In case you want to confirm the portno that SQL Server is listening on you can take a look at the startup section in the SQL Error Log and then look further for the section that follows " Server is listening on"
The information mentioned above is based on the following URL which provides comprehensive information for troubleshooting connectivity issues to SQL Server Database engine.