I got error (500 internal Server Error) in signing into my site collection…Actually I was trying to configure FBA in my sharepoint web Application that’s why I have made some changes in Web.Config of my web app and Central Admin, But now I have replace all the changes with default ones, But still my web application gives error…
The HTTP Error codes in the 500 range indicated the server was unable to access a required resource.
usually this is a database.
I assume, based on your post, you are just a client on the SharePoint site. The Sharepoint Administrator is the only one who can address this problem.
Http 500 errors actually indicate that the request got there but there was an error processing it on the server side. Many cases, especially in development and early deployment, this is due to database configurations. But it can be lots and lots of things in .NET as unhandled exceptions rightly stop flow.
Have you checked the SharePoint logs? That would be a great place to start.
ULS viewer is a good resource to achieve this, assuming you have access to the logs.