Private Sub Form_Load()
    HookForm Me.hwnd
End Sub

Private Sub Form_Unload(Cancel As Integer)
    UnHookForm Me.hwnd
End Sub

Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Public Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Public Declare Function GetLogicalDrives Lib "kernel32" () As Long
Public Declare Function GetDriveType Lib "kernel32" Alias "GetDriveTypeA" (ByVal nDrive As String) As Long

Public Const GWL_WNDPROC = -4
Public Const WM_DEVICECHANGE As Long = 537              'Cambios en un dispositivo
Public Const DBT_DEVICEARRIVAL As Long = 32768          'Cuando se conecta uno nuevo
Public Const DBT_DEVICEREMOVECOMPLETE As Long = 32772   'Cuando se desconecta uno
Public Const DRIVE_REMOVABLE As Integer = 2
Dim PrevProc As Long

Public Sub HookForm(hwnd As Long)
    PrevProc = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf WindowProc)
End Sub

Public Sub UnHookForm(hwnd As Long)
    SetWindowLong hwnd, GWL_WNDPROC, PrevProc
End Sub

Public Function WindowProc(ByVal hwnd As Long, ByVal uMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
    WindowProc = CallWindowProc(PrevProc, hwnd, uMsg, wParam, lParam)
    If uMsg = WM_DEVICECHANGE And wParam = DBT_DEVICEARRIVAL Then
        MsgBox USBConected
    End If
End Function

Public Function USBConected() As String
    Dim hVolume As Long, i As Integer
    hVolume = GetLogicalDrives()
    For i = 0 To 25
        If (hVolume And 2 ^ i) <> 0 And GetDriveType(Chr(i + 65) & ":") = DRIVE_REMOVABLE Then
            USBConected = Chr(i + 65) & ":"
        End If
    Next
End Function