Multiple function not performing

Can anyone help me with a formula? Here's what I have and need:
J2 contains amount ($10).
K2 contains current year fees due amount ($120)
L2 contains new balance ($130) (by formula sum=J2+K2
M2 contains last payment amount ($10)
N2 contains last mayment date, always changing, can be 2010 or 2011.

Here's where I need the formula...

O2 If the date in N2 is after 1/1/2011 then sum:L2-M2. If not, then give sum (or total) in L2

Sample workbook attached