In some cases, the McAfee application is configured to delete the files that it added to quarantine or clean them and restore as necessary. That's why you don't see the files in that section anymore. To access Quarantine, open McAfee, then click on Navigation > Quarantined and Trusted Items. Open Quarantined Items (individual files) or Quarantined Potentially Unwanted Programs (for programs).
Note: If the file is there, do not remove it from Quarantine unless you are 100 % sure it was a mistake, else you will be facing malware infection on your computer.