I created a Login but i need some help, can somebody explain/show the a best way to doing it, whit error validation like "Database invalid "/"This user don't exists".

See more:

VB

Visual-Studio

VS2012

...Hello everyone!
..i am new at this and is very hard to understand it, for some of you is very obvious but for me its hard to build the code,can you help me plz, i will appreciated.

Dim nome As Object

        name = Database.ExecuteScalar("SELECT a.name FROM users a   WHERE a.coduser = :pLogin and a.password = :pPassword" _ , myParamArray)
        Dim a As String      
        Dim b As String
        Dim errlist As String
        Try

            If Not name Is Nothing Then
                MsgBox("Welcome " & name.ToString & "!")
            Else
                 errlist
            End If

            Select Case errlist
                Case 1
                    If name = "" And passid = "" Then
                        MsgBox("enter the name and password")
                    End If
                Case 2
                    If name <> a Then
                    MsgBox("the name you entered does not exist, please enter a valid name.")
                    End If
                Case 3
                    if pass<> nome,b then
                    MsgBox("the password is incorrect")
                    End If
                Case 4
                    If name <> a And passid <> b Then
                   MsgBox("the user and password are incorrect, please insert again.")
                  End If
                Case 5
                    If DataBase = 0 Then
                    MsgBox("DB currently unavailable")    
                  ElseIf  Database = 1 Then
                        'works
                    End If

            End Select

        Catch ex As Exception
            MessageBox.Show("Error establishing a database connection:" + ex.Message)

        End Try