Hi,
One way: use a couple of event macros in the sheet window of the VBA editor.
Firstly:

Private Sub Worksheet_Activate()
Range("B2").Select
End Sub

Next:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Application.EnableEvents = False
If Range("B2") = "" Then
Range("B2").Select
MsgBox "You must enter something into B2"
End If
Application.EnableEvents = True
End Sub

Regards - Dave.