If you want to reactivate a campaign you previously archived, you can do so by following these steps:

1. Click on the "Campaigns" icon in the top, right of the page and then click on "Archived" in the box on the left of the screen to pull up a list of your Archived Campaigns.

2.  Check the box to the left of the Campaign you want to Activate and then click on the stopwatch icon.  This will Activate your Campaign.

You can view all of your Activate Campaigns by going to the Campaign page and clicking on "Active" in the box on the left of the screen.