Problem:
This is another common error that troubles plenty of ASP.NET users. Generally, the questions are framed like: “This error (HTTP 500 Internal Server Error) means that the website you are visiting had a server problem which prevented the webpage from displaying”
Or you can see on the picture below:

What is a 500 Internal Server Error?

In short, a HTTP 500 error implies that there's a drag with the configuration of the server. An HTTP 500 error isn't a problem the end user will solve themselves.  In their case, they need to report the matter to the server administrator or web site owner. however if you're managing your own IIS server and it’s your job to diagnose 500 server errors, there are many ways that to create the method easier.

Why am I getting HTTP 500 Internal Server Error IIS error?

The HTTP 500 Internal Server Error Iis error is also caused by windows system files harm. The corrupted system files entries may be a true threat to the well being of your PC.
There may be several events which can have resulted within the system files errors. an incomplete installation, an incomplete uninstall, improper deletion of applications or hardware. It also can be caused if your PC is recovered from a virus or adware/spyware attack or by an improper closedown of the PC. All the above actives could lead to the deletion or corruption of the entries within the windows system files. This corrupted system file can cause the missing and incorrectly joined info and files required for the right operating of the application.

How to Fix “HTTP 500 Internal Server Errors”
1. First, log on as an administrator
2. Then, Click the Start button -> All Programs -> Accessories -> System Tools, and then click System Restore.
3. On new window, choose the "Restore my computer to an earlier time" choice so click Next button.
4. choose the most recent system restore purpose from the "On this list, click a restore point" list, so click Next.
5. Click Next on the confirmation window.
6. Now, Restarts your Computer when the restoration is finished.