Logical Operators in Excel: If Not

I'm new in Excel VBA programming and I am trying to do the following within a Macro:

If Not Sheets(Currencies).Range("B2") = "USD" Then
    Sheets("Currencies").Range("B3").Formula = "=USD"
        Call Sheet3.UpdateCurrencyList
    Else
End If

I get runtime 5 error all the time and I simply cannot figure out how to solve it. Any help would be of much appreciation.