Cannot connect to SQLExpress

My C# app has problems connecting to my SQLServerExpress instance.

Running the app using localhost\SQLExpress or <servername>\SQLExpress in my connection string works locally on the server but not from other hosts in the network.

• I've already added a firewall rule for port 1433.
• AllowRemoteConnection is set to true.

I still get an SqlException saying:

System.Data.SqlClient.SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections.
System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, DbConnectionPool pool, String accessToken, Boolean applyTransientFaultHandling)
   at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnectionPool pool, DbConnection owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
   at System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.Open()

Is there anything else I need to check ?

Update #1:

PS C:\Windows\system32> Get-Process -Name sqlservr 
                        | Select-Object -ExpandProperty ID 
                        | ForEach-Object {Get-NetTCPConnection -OwningProcess $_ -state LISTEN 
                        | select LocalAddress, LocalPort, RemoteAddress, RemotePort, State}


LocalAddress  : ::
LocalPort     : 58956
RemoteAddress : ::
RemotePort    : 0
State         : Listen

LocalAddress  : ::
LocalPort     : 1433
RemoteAddress : ::
RemotePort    : 0
State         : Listen

LocalAddress  : 0.0.0.0
LocalPort     : 58956
RemoteAddress : 0.0.0.0
RemotePort    : 0
State         : Listen

LocalAddress  : 0.0.0.0
LocalPort     : 1433
RemoteAddress : 0.0.0.0
RemotePort    : 0
State         : Listen

Try this:

1. Go to SQL server configuration Manager (Win+R => SQLServerManager10.msc or SQLServerManager.msc)

2. Click SQL Network Services and navigate to concerned Server.

3. Enable TCP/IP Protocol for IP Based Conn (or) Named pipes for named connections(using server name)

4. Restart the SQL Server and Check