Thank you for the post and I apologize for the delay.
First, uninstall and reinstall with the FileMaker Server 12.0v4 full installer:
Afterwards, update to FileMaker Server 12.0v5:
Unless this installation resides on a Mac OS X 10.9 Mavericks machine, then use the FileMaker Server 12.0v6 full installer:
Please let me know if any of the above requires additional clarification.