My old pipelines have disappeared
If your project was set up some time ago and you have triggered builds on CircleCI, you might find that you cannot see these older pipelines anymore but see a "Set up configuration to start running pipelines" message on the project page instead.
Data retention policy
The reason why the "Set up configuration to start running pipelines" message appears, is that there is currently no build history to display on the UI.
As per our data retention policy, build history is kept for a certain amount of days based on your plan. You can find more about the data retention policy here.
If your last build falls outside of the data retention window and you haven't triggered a new build by pushing a commit or opening a pull request since, no pipeline will be available to view.
I can't set up the configuration again
Even though no build history is available because you haven't built on the project for longer than the data retention window, the project settings are still in place.
Please try to push a commit or open a pull request. Since the project has already been set up, this should trigger a new build, which will appear on the project's page.