Check To See If Dates Match In Two Separate Columns?

what i am trying to do is look at an entire column, and see if that same date exists in the other Activity tab, if the dates match, then show the activity

here is the formula i am using, =IF($A9=Activity!$A2,Activity!$B2,"No Activity")

my problem is that i am only able to isolate one of the cells,, how do i check the entire column?

in other words, if i select two weeks, those two weeks of activity will show, if i select all weeks, all of the weeks activity will show, right now i can only get one of the weeks

my data looks like the following

1st tab
1/8/2013 - 1/14/2013
1/29/2013 - 2/4/2013
1/22/2013 - 1/28/2013

[Code].....