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You can check the status of your CE site here and restart if it is down, if it is deactivated then I'm afraid there is any solution to it other than contacting community@appian.com.
In case you have restarted it already then just FYI, they are facing high request volumes these days so it is taking more time than usual in fulfilling the requests but don't worry your site will restart in about a week max with all of your work restored.