Thank you all.
I basically want the textbox to behave as a number cell. Like Excel or a datagridview.
But a textbox is designed for text.
I think I figured out a workaround.

HTML Code:
    Dim EnteringTxtBox As Boolean
    Private Sub TextBoxes_Enter(sender As Object, e As EventArgs) Handles TextBox3.Enter, TextBox2.Enter, TextBox1.Enter
        EnteringTxtBox = True
    End Sub
    Private Sub TextBox1_Click(sender As Object, e As EventArgs) Handles TextBox1.Click, TextBox2.Click, TextBox3.Click
        If EnteringTxtBox Then
            DirectCast(sender, TextBox).SelectAll()
            EnteringTxtBox = False
        End If
    End Sub