Fix WordPress When Maintenance Mode Is Stuck
WordPress updates and upgrades are very common, both for the core of WordPress as well as the many themes and plugins that are used. WordPress has a built in feature to set the website into "Maintenance Mode" during these updates and upgrades. While that is a great idea and quite helpful at times, it can also be a problem in the event that an update or upgrade fails. In the normal process of an upgrade Maintenance Mode is turned off once the upgrade has finished. However, if an upgrade fails, Maintenance Mode will be stuck on until it is manually turned off.
Thankfully, fixing this problem is quite easy. WordPress simply creates a file named ".maintenance" in your sites root directory to enable Maintenance Mode. To manually turn Maintenance Mode off and fix the problem, you simply delete that file (typically by logging onto your site's FTP server) from the root directory. Once the file has been deleted WordPress will load normally. WordPress has a short how to on this topic as well as a WordPress Codex Article.