flex builder 3 problem

Question

i am using flex builder 3.I have this simple practice app.it's a whenever I click the green button at the top of the IDE, ofcourse it will pop out the window of the app..I canged the tag to , when i clicked the green button, it didn't pop out the window....now the problem is, when i reverted it back to the former, the window doesn't pop out anymore, even if I restart the IDE itself...it only works if I restart the machine....do you know how trouble shoot this in flex builder 3? ..do I need to shut down any processes in the task manager in order to make the popping out of window work again without restarting the machine?