Multiple Criteria for an IF Statement

Hi there,

I need some help with the following, please


Column "D" represents Start Date
Column "E" represents End Date

12 months range i.e. 01/08/2011 (Cell S1) & 31/07/2012 (Cell T1)

I would like formula in Column "R" to show "Yes" if

the date in D is older than "S1" i.e Cell D10 = "15/07/2011"

or

the date in E is newer than "T1" or empty i.e Cell E10="" or "10/08/2012



Hope this makes sense.


Appreciate your help.


PS


My current formula is not returning any answers

=IF(OR(AND($D20<$S$1,$E20>$T$1),AND($D20<$S$1,$E20=""),"YES",""))