This will work for you just great! First add reference to System.Management and then make sure to import it at the top of your class as well. I did this on a form load event, but you can put it anywhere...
Imports System.Management
Dim q As New SelectQuery("Win32_bios")
Dim search As New ManagementObjectSearcher(q)
Dim info As New ManagementObject
For Each info In search.Get
MessageBox.Show("Serial Number: " & info("serialnumber").ToString & vbNewLine & vbNewLine & "Bios Version: " & info("version").ToString)
Next
You can declare a string first if you would like and then set it to: info("serialnumber").ToString and the set that to you txtSerial.Text = your declared string
Here is what I get...