Fix The website cannot display the page – HTTP 500 Internal Server Error in SharePoint

Problem: 
When I opened SharePoint 2013 Central Administration site, it returned an error message: HTTP 500 Internal Server Error: The website cannot display the page error message!

Troubleshooting:

• Check all required ports are open in Firewall in web & database servers.
• Update passwords on IIS Application Pool identities. Make sure they are not stopped or Offline. Update the identity password for “SecurityTokenServiceApplicationPool ” application pool and start it.
• In most cases, It’s due to web.config issues! Restore the web.config file from backups or create a dummy web app, copy-paste the web.config file from it.
• If your SharePoint Farm account password is changed/expired, Update it with: stsadm -o updatefarmcredentials -userlogin “domain\username” -password “password”
• Make sure IIS Web sites are running. SharePoint Timer service is running.
• If you are experiencing this issue with the SharePoint 2010 Central Administration site, try re-provision it:  How to Re-Provision SharePoint Central Admin Site. Try Running the SharePoint Configuration wizard again – don’t disconnect.
• It could be due to SQL Server issues! To check the database server connectivity issues, SQL Server instance is running in the Database server. Databases are accessible.
• Try Re-register Asp.net framework by running :C:\Windows\Microsoft.NET\Framework\<<.NET VERSION >>  aspnet_regiis.exe -iru
• Make sure your SharePoint setup account is added under the Administrator group of the server(s). 
•  If you get Event ID 8305 with an error message, “An exception occurred when trying to establish endpoint for context. An error occurred loading a configuration file. Either a required impersonation level was not provided, or the provided impersonation level is invalid.”, Here is the fix: Go to Start >> Administrative tools >> Local Security Policy >> Local Policies >> User Right Assignments – Impersonate a client after authentication properties >> Add the Application Pool account >> Restart the Server.
• Do a simple IIS Reset!