Thank you for the post.
Which version of FileMaker Server?
If using FileMaker Server 11 (Advanced) or FileMaker Server 12 (Advanced), then follow the instructions in the following knowledge base article:
Additionally, a power outage might have damaged the installation, so if the above doesn't lead to a resolution, then uninstall and reinstall FileMaker Server. After updating FileMaker Server as far as possible, run the patch in the article for the appropriate version to regain Admin Console access.
Please let me know if any of the above needs further clarification.