Keep completed tasks?
 

How do i keep omnifocus from deleting a task once it's marked as complete? I'm not sure if i've done something wrong, but I marked off a few tasks complete before I shut off my laptop last night, and when I turned it back on this morning the completed tasks were gone. I use omnifocus to organize my homework, and within the notes section of tasks I write references for my papers, so even though the task is complete, i still need access to the notes affiliated with the tasks, so I do not want omnifocus to delete the task once it has been completed.
Cheers

It doesn't delete the task when you mark it complete, it merely hides it from view (when using the default view settings). Turn on the View Bar (View->Show View Bar or cmd-shift-V), set the action selector (the third one from the left over the main outline) to Any Status and you will see all the actions whether completed or not.

You can also select "Completed Items" from the perspectives menu to see actions that you've marked off.