'text box for user input of the loan term and verifies the input values
    Private Sub txtLoanTerm_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtLoanTerm.TextChanged
 
        If Me.txtLoanTerm.Text <> "" Then
            If IsNumeric(txtLoanTerm.Text) Then     'checks input for numeric value
                If txtLoanTerm.Text > 0 Then        'checks input to make sure number entered is more than zero
                Else                                'show error if conditions are not met
                    MessageBox.Show("Input Error Please Enter a Numeric value Greater Than Zero")
                    Me.txtLoanTerm.Text = ""
                    Me.txtLoanTerm.Focus()
                End If
            Else                                    'show error if conditions are not met
                MessageBox.Show("Input Error Please enter a valid numeric value")
                Me.txtLoanTerm.Text = ""
                Me.txtLoanTerm.Focus()
            End If
        End If
 
    End Sub

Private Sub ValidateNumbers(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged, TextBox2.TextChanged, TextBox3.TextChanged
  Dim ThisBox As TextBox
 
  ThisBox = CType(sender, TextBox)
  If ThisBox.Text <> "" Then
    If IsNumeric(ThisBox.Text) Then     'checks input for numeric value
      If CDbl(ThisBox.Text) <= 0 Then   'checks input to make sure number entered is more than zero
      	'show error if conditions are not met
        MessageBox.Show("Input Error Please Enter a Numeric value Greater Than Zero")
        ThisBox.Text = ""
        ThisBox.Focus()
      End If
    Else                                    
    	'show error if conditions are not met
      MessageBox.Show("Input Error Please enter a valid numeric value")
      ThisBox.Text = ""
      ThisBox.Focus()
    End If
  End If
 
End Sub

Dim ErrMessage As String
 
If Lastname.Text ="" Then
    ErrMessage = ErrMessage & "Lastname must have a value." & NewLine
End If
 
If Firstname.Text ="" Then
    ErrMessage = ErrMessage & "Firstname must have a value." & NewLine
End If
 
MesagBox.Show(ErrMessage)

ElseIf ThisBox.Text.Trim = "" Then
                MessageBox.Show("Please press continue on the next screen" _
                & " and enter the missing information")
                ThisBox.Focus()      'Set focus to field 
            End If

Dim strInterestRate As String   'string from interest rate text box
        strInterestRate = Me.txtInterestRate.Text
        'checks to make sure the Interest Rate box is not left empyt
        If Me.txtInterestRate.Text.Trim = "" Then
            MessageBox.Show("Please press continue on the next screen" _
            & " and enter the 'Interest Rate'")
            Me.txtInterestRate.Focus()  'Set focus to field 
        End If

Private Sub ValidateNumbers(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged, TextBox2.TextChanged, TextBox3.TextChanged
  Dim ThisBox As TextBox
  Dim Msg As String
  ThisBox = CType(sender, TextBox)
  If ThisBox.Text <> "" Then
    If IsNumeric(ThisBox.Text) Then     'checks input for numeric value
      If CDbl(ThisBox.Text) > 0 Then        'checks input to make sure number entered is more than zero
      Else                                'show error if conditions are not met
        MessageBox.Show("Input Error Please Enter a Numeric value Greater Than Zero")
        ThisBox.Text = ""
        ThisBox.Focus()
      End If
    Else                                    'show error if conditions are not met
      MessageBox.Show("Input Error Please enter a valid numeric value")
      ThisBox.Text = ""
      ThisBox.Focus()
    End If
  Else ' HERE THE BOX IS EMPTY
    ' "Generic" solution
    MessageBox.Show("Please press continue on the next screen" _
      & " and enter the missing data")
    ThisBox.Focus()
    ' 2nd solution
    ' Since you want to identify exact box:
    Msg = ""
    If TextBox1.Text.Trim = "" Then
      Msg = "Interest rate"
    End If
    If TextBox2.Text.Trim = "" Then
      Msg = "Loan term"
    End If
    If TextBox3.Text.Trim = "" Then
      Msg = "This item"
    End If
    MessageBox.Show("Please press continue on the next screen" _
      & " and enter the '" & Msg & "'")
    ThisBox.Focus()
  End If
End Sub