Muchas gracias a todos por sus comentarios, he resuelto el problema, ha sido un poco frustrante saber programar y no poder verlo reflejado en el codigo debido a mi falta de practica en este lenguaje. escribo el codigo final.
Código:
Imports System.Data.SqlClient
Imports System.Text
Public Class bienvenido
Private Sub entrar_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles entrar.Click
Dim usuarioTmp As String = FixString(Trim(Me.usuario.Text), "'", "''")
Dim passwordTmp As String = FixString(Trim(Me.pass.Text), "'", "''")
Dim cnString As String = My.Settings.CGADSConnectionString
If usuarioTmp <> "" And passwordTmp <> "" Then
Dim flag As Boolean = True
Dim connection As New SqlConnection(cnString)
Try
connection.Open()
Catch ex As Exception
MsgBox("Error " & Err.Number & " :" & ex.Message)
End Try
Try
Dim cadena_comando As String = "SELECT pass FROM usuarios WHERE usuario='" & usuarioTmp & "' AND pass='" & passwordTmp & "'"
Dim command As SqlCommand = New SqlCommand(cadena_comando, connection)
Dim myPassword As String = Trim(command.ExecuteScalar().ToString)
Catch ex As Exception
flag = False
MsgBox("Ha ocurrido un error al momento de iniciar sesión.Intentelo mas tarde.")
Finally
connection.Close()
If flag = True Then
Dim pri As New principal
pri.Show()
If Not Me.Modal Then Me.Close()
End If
End Try
End If
End Sub
Private Function FixString(ByVal SourceString As String, ByVal StringToReplace As String, ByVal StringReplacement As String) As String
SourceString = SourceString.Replace(StringToReplace, StringReplacement)
Return SourceString
End Function
End Class