Как ввести запрет на ввод букв в TextBox - Visual Basic .NET

Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim i As Integer
        i = 0
        If TextBox1.Text <> "" Then i = i + 1
        If Val(TextBox1.Text) > 0 Then i = i + 1
        If Val(TextBox1.Text) < 100 Then i = i + 1
        If TextBox1.Text = "" Then
            MsgBox("Введите число")
        End If
        If Val(TextBox1.Text) < 0 Then
            MsgBox("МЕНЬШЕ НУЛЯ, ХИТРЕЦ")
        End If
        If Val(TextBox1.Text) > 100 Then
            MsgBox("Куда так много?! не больше 100!")
        End If
        If RadioButton1.Checked = False And RadioButton2.Checked = False And RadioButton3.Checked = False Then
            MsgBox("УРОВЕНЬ ВЫБЕРИ")
        End If
        If RadioButton1.Checked = True Then
 
        End If
        Dim Therandom As New Random
        If i = 3 Then
            If RadioButton1.Checked = True Then
                If TextBox1.Text > 10 Then
                    MsgBox("Число не должно быть больше 10")
                ElseIf TextBox1.Text < 11 Then
                    Label1.Visible = False
                    Label2.Visible = False
                    Label3.Visible = False
                    Label1.Text = Therandom.Next(1, 10)
                    If TextBox1.Text = Label1.Text Then
                        Label1.Visible = True
                        Label2.Visible = True
                        Label3.Visible = True
                        Label3.Text = "YOU ARE CORRECT!!"
                        Button1.Enabled = False
                        TextBox1.Enabled = False
                    Else
                        Label1.Visible = True
                        Label2.Visible = True
                        Label3.Visible = True
                        Label3.Text = "YOU LOSE!!"
                        Button1.Enabled = False
                        TextBox1.Enabled = False
                    End If
                End If
            ElseIf RadioButton2.Checked = True Then
                If TextBox1.Text > 50 Then
                    MsgBox("Число не должно быть больше 50")
                ElseIf TextBox1.Text < 51 Then
                    Label1.Visible = False
                    Label2.Visible = False
                    Label3.Visible = False
                    Label1.Text = Therandom.Next(1, 50)
                    If TextBox1.Text = Label1.Text Then
                        Label1.Visible = True
                        Label2.Visible = True
                        Label3.Visible = True
                        Label3.Text = "YOU ARE CORRECT!!"
                        Button1.Enabled = False
                        TextBox1.Enabled = False
                    Else
                        Label1.Visible = True
                        Label2.Visible = True
                        Label3.Visible = True
                        Label3.Text = "YOU LOSE!!"
                        Button1.Enabled = False
                        TextBox1.Enabled = False
                    End If
                End If
            ElseIf RadioButton3.Checked = True Then
                If TextBox1.Text > 100 Then
                    MsgBox("Число не должно быть больше 100")
                ElseIf TextBox1.Text < 101 Then
                    Label1.Visible = False
                    Label2.Visible = False
                    Label3.Visible = False
                    Label1.Text = Therandom.Next(1, 100)
                    If TextBox1.Text = Label1.Text Then
                        Label1.Visible = True
                        Label2.Visible = True
                        Label3.Visible = True
                        Label3.Text = "YOU ARE CORRECT!!"
                        Button1.Enabled = False
                        TextBox1.Enabled = False
                    Else
                        Label1.Visible = True
                        Label2.Visible = True
                        Label3.Visible = True
                        Label3.Text = "YOU LOSE!!"
                        Button1.Enabled = False
                        TextBox1.Enabled = False
                    End If
                End If
            End If
        End If
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        TextBox1.Enabled = True
        Button1.Enabled = True
    End Sub
End Class