Code Which Includes Many IF

I have the following vba code which serves essentially to find the serial number of the computer's hard disc. When the code find the serial number then can be avaliable as "S" to use it as you may want. Now, if you assign any Pc as the "Administrator" (through the vba code) after the verification of the serial number the code should by-pass all relevant procedures and proceeds directly to open the form "frmStartupScreen".

The Problem: Although the code works, sometimes (not always) after the opening of the database cannot show the relevant messages ( eg. "Welcome Administrator" if the code recognize the Pc as the administrator) and leaves the empty the screen (blue screen environment access) and i must do even a click anywhere in order to show the relative messages so to be able to Login the database. Is it something related to my computer ? Maybe it would be better instead of the code "IF" to change it with "Case" ? If with "Case" should be better.

Public Function CheckVolumeSerialNumber1()
Dim S, Serial As Long, VName As String, FSName As String, strSQL As String
VName = String$(255, Chr$(0))
FSName = String$(255, Chr$(0))

[code]....