1. Check to see if the sites have been made available for synchronization.
2. Make sure you have the latest version of OneDrive installed and that you are logged in properly.
3. Make sure there is enough space on your local hard drive to store the documents.
4. Confirm that any other cloud-based programs are not interfering with sync.
5. Restart the sync process by signing out of all cloud-based programs and then signing back in.
6. Try syncing via an external network if one is available.
7. Submit a ticket and obtain assistance to diagnose the issue.