I'll show you fast and easy way to get operating system serial number that the application is running on. Here how to accomplish this task:

In Page_Load event handler (for example) getting WSN:

Dim MOS As ManagementObjectSearcher = New ManagementObjectSearcher("Select * From Win32_OperatingSystem")
Dim MO As System.Management.ManagementObject
Dim MOC As System.Management.ManagementObjectCollection = MOS.Get
Dim WindowsSerial As String = String.Empty

For Each MO In MOC
WindowsSerial = MO("SerialNumber")
Next