I have been unable to access the SharePoint server central administration page for almost a month.
The central administration page worked very well. But for a month, the SharePoint sites and the central administration page stopped working.
The last modification I had to make is the change of the password of the administrator account. The problems started after and I don't know what to do.
Update:
SharePoint Configuration Wizard error message displayed:
Failed to upgrade SharePoint Products. This is a critical task. You have to fix the failures before you can continue. Follow this link for more information about how to troubleshoot upgrade failures: https://go.microsoft.com/fwlink/?LinkId=866803
An exception of type Microsoft.SharePoint.PostSetupConfiguration.PostSetupConfigurationTaskException was thrown. Additional exception information: Upgrade [SpContentDatabase Name=WSS_Content] failed. (EventID:an59t) Exception: The upgraded database schema doesn't match the TargetSchema (EventID:an59t) (EventID:an59t) Upgrade Timer job is existing due to exception: Microsoft.Sharepoint.Upgrade.SPUpgradeException: The upgraded database schema doesn't match the TargetSchema*