Disable button if more textboxs are empty or input text

[alee001]

Hello, I want to disable a OK command button if 3no textboxs are empty or input any text(non-number),
with ISTextBox.value<=OOSTextBox.value. I write the code as following but not work at same time by all textboxs,
what wrong and how to do it? thanks and help.....
P.S. I had take false on enable item of OK command button

Private Sub dayTextBox_Change()
If dayTextBox.Value = 0 Or dayTextBox.Value = "" Then
    OKCommandButton.Enabled = False
Else
    OKCommandButton.Enabled = True
End If
End Sub
+
Private Sub ISTextBox_Change()
If ISTextBox.Value = 0 Or ISTextBox.Value = "" Then
    OKCommandButton.Enabled = False
Else
    OKCommandButton.Enabled = True
End If
End Sub
+
Private Sub OOSTextBox_Change()
If OOSTextBox.Value = 0 Or OOSTextBox.Value = "" and _
    ISTextBox.value <= OOSTextBox.value Then
    OKCommandButton.Enabled = False
Else
    OKCommandButton.Enabled = True
End If
End Sub