Welcome to the forum.
I suspect that the event handler is being called but that your logical check has a flaw: the address should have an uppercase "B". Also, there's no need to select the rows to autofit them using code.
Code:
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$B$5" Then
Me.Rows("10:61").EntireRow.AutoFit
End If
End Sub
An easy way to tell if your event handler is being called is to add a breakpoint. If you find it is not being called then it probably means that events have been disabled. To re-enable them type this into the immediate window:
Code:
Application.EnableEvents=True
However, I think it is most likely that the problem was the lower case "b" in the code you posted.
Hope that helps...