Cannot telnet SQL Server port 1433
Here's a powershell script I wrote for checking connectivity to SQL servers as you are using the default port (1433) all you need to do is pass in the server name.  If the connection fails the exception should give you a clue as to why.

e.g. 
CheckSql.ps1 server\instance 

CheckSql.ps1

param([Parameter(Mandatory=$true,ValueFromPipeline=$true)][string]$serverInstance);

$connectionString = "Data Source={0};Integrated Security=true;Application Name=CheckSQL.ps1" -f $serverInstance;
$sqlConn = new-object("Data.SqlClient.SQLConnection") $connectionString;

Write-Host $connectionString

try {
    $sqlConn.Open();
    $sqlConn.Close();
    Write-Host "Connected OK"-foregroundcolor white -backgroundcolor green
}
catch { 
    Write-Host $_ -foregroundcolor white -backgroundcolor red
}
finally { 
    $sqlConn.Dispose(); 
}