Turnitin have recently released a new version of their iPad app.
They advise that users should go into the app and manually sync before upgrading to the latest version of the app. If you do not do this, you may just see a black screen after upgrading.
How to sync is described here:
It is also possible to uninstall and then reinstall the app which will move you past the black screen. However, if you uninstall the app, any unsynced data will be lost and is unrecoverable.
The new app supports the recently introduced Turnitin features.