Logical Dates - OVERDUE

Hi,,

I need to track when a request is 'OVERDUE', for example

Date Received Date Sent Out OVERDUE

19/06/15 dd/mm/yy

From date received to date sent out should be under '5 days',,if this isn't the case, in some cases the 'Date Sent Out cell will be blank, then I need the Date Sent out cell (or another on the same line, it doesn't matter) to state 'OVERDUE'

I've tried the =IF statement, but get 'invalid',,I've been thinking of using a comparison date i.e.=TODAY(), but don't know where to fit it in in the formula, again I get 'Invalid'

I do hope this is clear, if not let me know,

Any help would be much appreciated,,

Regards,

Kev