Guys, I already solve my own problem using this code.
Thanks.
Code:
Private Sub CommandButton2_Click()
Dim form As String
form = cmbForm.Value

If txtFrom.Value = "" Then
MsgBox "Type Start Page"

ElseIf txtTo.Value = "" Then
MsgBox "Type End Page"

ElseIf txtCopy.Value = "" Then
MsgBox "Type Number of Copies"

Else
Worksheets(form).PrintOut Preview:=True, From:=txtFrom.Value, To:=txtTo.Value, Copies:=txtCopy.Value
End If
End Sub